FIREARM ACCESSORY CLAMP MOUNT HAVING ROTATABLE LOCKING LEVER AND LOWER ADJUSTMENT NUT

Abstract

An adjustable accessory mounting mechanism for firearms has an accessory mount rail having clamp surfaces. A mount base member has a clamp structure in retaining engagement with the clamp surfaces and supports a clamp plate member for rotary clamping engagement with the accessory mount rail. A clamp retainer screw extends through the retainer opening and pivotally supports the clamp plate member for rotary locking and unlocking movement. An adjustment nut member is threaded to the clamp retainer screw and adjusts the position of the clamp plate member. The adjustment nut is located below the lower surface of the clamp plate and clamp support to prevent its catching on brush, vines and other objects during field use.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a lever actuated clamp mechanism for mounting an accessory, such as a sighting device or other implement, to an accessory mount rail of a firearm. More particularly the present invention concerns an accessory mount base having a rotatable locking lever actuated clamp mechanism, with the locking lever thereof pivotally mounted beneath the mount base structure. Even more particularly, the present invention concerns a lever actuated clamping mechanism wherein a locking lever and a locking cam plate are in the form of an integral locking unit which is pivotally secured by a single retainer screw to a support platform of the mount base structure. The present invention provides an adjustment nut which is threaded to the retainer screw and is located below the locking platform, thereby ensuring that the upper portion of the locking platform is substantially unobstructed and is unlikely to become fouled by dirt, mud and the like, or caught on brush, vines and other impediments as the firearm is used in a field environment.

2. Description of the Prior Art

It is often desired to provide for attachment and support of an accessory device on a supporting object, such as a firearm. In the field concerning firearms, accessories, including optical sighting devices, manual sighting devices, light emitting devices, firearm handgrips, and the like, are often mounted to various types of firearms to enhance the firearm sighting and handling capability of a user.

Accessory devices, such as mechanical and optical sighting devices have historically been mounted to the receiver or barrel of a firearm by means of mounting screws. This is typically referred to as a permanent mount since the accessory will typically remain in assembly with the firearm until the firearm or the accessory needs replacement or repair. A number of quick-release type mount clamping systems have been developed over the years which permit an accessory to be quickly assembled to or removed from a firearm. These quick-release mounting systems are generally quite effective, though several of the known quick-release mounting systems suffer from the standpoint of accuracy. Also, many of the quick-release sight mounts for firearms define projecting components that tend to catch on brush, plants and other objects as a firearm is being carried by a user. It is desirable therefore to provide an accessory mount mechanism for firearm that provides a clean and substantially unobstructed upper portion that eliminates or minimizes the potential for catching and becoming tangled as the firearm is carried in a field environment that is wooded or contains brush, vines and other growth.

It is desirable to provide an accessory mount and clamp mechanism that permits users to remove and replace various accessories, even during field conditions, without any need for tools or through the use of simple and efficient tools. It is also desirable to provide users with the capability of easily adjusting the clamping force that is being applied to a mount rail so that a user can increase, decrease or repeatedly employ substantially the same clamping force each time an accessory is removed from a firearm and is then replaced. This is especially important in the field of firearms where sighting devices can be removed from the mounting rail of a firearm and re-installed in a manner that causes the sighting device to return to its pre-set zero when it is again clamped to its former location on an accessory mounting rail. It is also desirable to provide an accessory mount that provides a clean and unobstructed upper surface that minimizes any tendency of the accessory mount system becoming fouled by catching on objects as a firearm is carried and by accumulations of dirt, mud and other debris that is likely to be encountered during use of a firearm in field conditions.

SUMMARY OF THE INVENTION

It is a principal feature of the present invention to provide a novel accessory mount and clamp mechanism for firearm accessory mounts and for mounting accessories to other apparatus, such as cameras, camera lenses, spotting telescopes, astronomical telescopes and the like to the mount rails of tripods or other supporting apparatus.

It is another feature of the present invention to provide a novel accessory mount and clamp mechanism which facilitates assembly or disassembly of an accessory support mount from a mounting rail of a supporting device, even in poor light conditions or other field conditions without risk of separating and losing any of the components of the clamp mechanism.

Briefly, the various objects and features of the present invention are realized by a clamp actuated accessory mounting system that is designed particularly for mounting various accessories, such as optical firearm sighting devices, spotting telescopes, and the like, to accessory mounting rails such as Picatinny rails, Weaver rails or other similar mounting rail systems for firearms, photography equipment astronomy telescopes and the like. The present invention incorporates a clamp base structure having a portion that is configured for clamping engagement with elongate, oppositely facing, tapered and undercut surfaces of an accessory mounting rail. The clamp base structure defines one or more laterally projecting clamp platforms or supports, each defining a clamp actuator opening.

A hardened bushing member is seated within the clamp actuator opening and defines a clamp actuator receptacle within which a clamp retainer screw or bolt is received. The clamp retainer screw has a shank or shaft that extends through an opening of a clamp plate member that is in the form of a cam plate, having an elongate tapered peripheral cam surface that is disposed for cam force transmitting engagement with a tapered clamp surface of an accessory mount rail. The shaft of the clamp retainer screw defines a non-circular section which is received by a corresponding non-circular opening of the cam plate member, thus permitting linear movement of the cam plate member relative to the retainer screw, but preventing rotation of the cam plate member relative to the retainer screw.

An annular spring member, such as a circular wave spring, is positioned about the shaft of the retainer screw and applies spring force to the head of the retainer screw and to the upper surface of the cam plate member. This spring force urges the cam plate member downwardly and ensures that the cam plate member is maintained in engagement with an adjustment nut member that is threaded to the lower end of the shaft of the retainer screw. For adjusting the position of the cam plate member to change its cam energized clamping force against a tapered clamp surface of an accessory mounting rail, the adjustment nut is rotated, thus moving the cam plate member linearly with respect to the non-circular section of the shaft of the retainer screw or permitting spring energized movement of the cam plate member relative to the retainer screw shaft, depending on the direction of rotation of the adjustment nut. This arrangement permits precision adjustment of the clamping force so that the clamp mechanism can be securely tightened, without causing any deformation of the tapered clamp surface of the accessory mounting rail.

To provide a light weight accessory mount mechanism, such as for firearms, the mounting base and the support rings of the sight mounting system is preferably composed of a light-weight material such an aluminum alloy, hard polymer material or the like. However, if desired, the mounting base can be machined from hardened and more durable material such as steel, stainless steel, titanium or the like, when strength and durability are critical considerations. The mounting base, regardless of the material from which it is constructed, is drilled or otherwise formed to eliminate material and minimize the weight thereof. Since light-weight metal materials are often quite soft and easily yielded by application of forces, hardened metal inserts composed of stainless steel, steel or other suitable hard materials are press-fitted or otherwise seated in appropriate openings or receptacles of the mount structure. These inserts are typically threaded so as to have threaded engagement with retainer elements such as Torx or Allen screws. If desired however, the inserts may simply be press-fitted within insert receptacles and/or may be seated on internal seat shoulders if forces are not present that would otherwise tend to separate an insert from its receptacle.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features, advantages and objects of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the preferred embodiment thereof which is illustrated in the appended drawings, which drawings are incorporated as a part hereof.

It is to be noted however, that the appended drawings illustrate only a typical embodiment of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

In the Drawings:

FIG. 1 is a side elevation view showing an a tactical firearm having an accessory mounting rail and having an accessory mount and clamp mechanism embodying the principles of the present invention mounted thereto and supporting an optical sighting device;

FIG. 2 is a top view showing the accessory mount and clamp mechanism being of FIG. 1;

FIG. 3 is a front elevation view showing the accessory mount and clamp mechanism of FIG. 2 in greater detail;

FIG. 4 is a section view taken along line 4-4 of FIG. 2, showing the lever actuated pivotal clamp mechanism thereof in detail;

FIG. 5 is an exploded isometric illustration showing a mount base for dual lever actuated clamping mechanisms, and showing one of the clamping mechanisms and a pivot mount opening for receiving an identical or similar lever actuated clamping mechanism; and

FIG. 6 is an exploded isometric illustration showing the locking cam plate pivot mechanism in detail and, together with FIG. 5, representing the preferred embodiment and best mode of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Referring now to the drawings and first to FIG. 1, a firearm in the form of a tactical rifle is shown generally at 10, and incorporates an upper receiver 12, being in pivotal assembly with a lower receiver 14 at a pivot 16. A firearm barrel 18 is mounted to the upper receiver 12 and a major portion of the barrel is enclosed within an internal cavity of a handguard 20. The handguard is shown to be mounted to the upper receiver 12 by means of a flanged connection 22 having abutting mounting flanges that are secured in releasable assembly by a plurality of retainer screws or by other suitable means for retention.

The upper receiver 12 and the handguard 20 are each provided with accessory mounting rail sections 24 and 26, each having a multiplicity of evenly spaced ribs or ridges and grooves or spaces. Accessory mounting rails, typically referred to as Picatinny rails or Weaver rails, were developed many years ago and are generally widely accepted in the tactical firearms industry for releasably mounting a wide range of sighting devices, target illumination devices, and various types of accessory mounts to a firearm. Accessory mounting rails for firearm sighting devices typically project upwardly, as viewed in FIG. 1, and are aligned with the center-line of the bore of the barrel of a firearm to provide for mounting optical and mechanical sighting devices, such as the telescope 28 shown in FIG. 1, to the structure of a firearm. Precise alignment of the mounting rails with respect to the barrel of a firearm promotes the efficiency and accuracy of aiming and shooting activities. The handguards and other components of typical tactical rifle systems also incorporate accessory mounting rails that project laterally and/or downwardly from the handguard or other firearm component and permit the mounting of various other devices to the structure of the firearm. For example, in FIG. 1 a bipod 30 is shown to be mounted to a downwardly projecting accessory mounting rail section 32 of the handguard 20. Laterally projecting mounting rail sections 34 also extend from the handguard structure and provide means for releasable attachment of lasers and various other illumination devices to a firearm to promote aiming and shooting during conditions of minimal light.

Referring now particularly to FIGS. 2 and 3 a lever actuated accessory mounting and clamping mechanism shown generally at 40 incorporates a mount base 42 having an upper mount structure 44 that can have any suitable form for attachment of an accessory device thereto. The mount base 42 is preferably composed of a lightweight metal such as an aluminum alloy to minimize weight without any sacrifice from the standpoint of strength and durability. As shown in FIGS. 2-4 the upper mount structure 44 is shown as a simple structural member having openings 46 to receive various types of retainer devices to secure various types of accessories to the mount base structure. However, it is to be borne in mind that the upper mount base structure may have any of a number of suitable forms that effectively tailor the mount base for the specific accessory device that it is intended to support.

The mount base 42 is provided with spaced lateral clamp flange members 48 and 50 that define downwardly and outwardly angulated planar surfaces 52 and 54 that form a cavity of a configuration matching the external geometry of an accessory mount rail which is shown in broken lines in FIG. 4. The lateral clamp flange member 50 defines an oppositely angulated planar undercut surface 56 that intersects the oppositely angulated planar surface 54 and defines an internal profile that matches a portion of an accessory mounting rail. One or more locator keys 58 project downwardly from the lower surface portion of the mount base structure 42 and are oriented to enter one or more spaced slots or recesses that are defined by an accessory mounting rail of a firearm, thus selectively locating the accessory mount mechanism on a mounting rail and at a position that is specific to the needs and comfort of a firearm user.

As shown in FIGS. 2, 3 and 5 an accessory mount base may be designed to incorporate a pair of spaced lever actuated clamping mechanisms. However, if desired, an accessory mount mechanism may have one, two, three or more lever actuated clamping mechanisms, depending on the use which the accessory mount is to serve. For example, to accommodate the severe recoil of firearms shooting .50 caliber cartridges, a sight mount mechanism may have three or four lever actuated clamping mechanisms while firearms handling standard 5.56 mm cartridges may employ a sight mount mechanism having only a single lever actuated clamping mechanism. The accessory mounting systems typically employ a number of lever actuated cam locking systems that is dependent on the weight or mass of the accessory and the force that is to be applied to the accessory during use of a firearm. The mount base 42, as shown in FIGS. 1-3 and 5, is provided with two spaced clamp support platforms 60 and 62. Each of the clamp support platforms defines a circular opening 64 having an upwardly facing annular internal support shoulder 66 as shown in FIGS. 4 and 5.

A circular bushing insert member 68, composed of a hard and durable material such as steel, stainless steel, etc., is positioned within the circular opening 64 and defines a downwardly facing annular shoulder 70 that is seated on the annular internal support shoulder 66 of the mount base platform. The circular bushing insert member is preferably press-fitted within the circular opening 64; however, it may be retained within the circular opening by a close fit or by any other suitable means. The lower end 72 of the circular bushing insert member 68 projects slightly beyond the downwardly facing planar surface 74, and when engaged by the locking cam plate, provides for spacing of the upper planar surface of a locking cam plate from the lower planar surface of the platforms 60 and 62 as is discussed in greater detail below. In one form of the invention, a circular support washer member 76 is positioned within a circular opening that is defined by the circular insert member 68 and is seated on an annular upwardly facing internal shoulder 78 of the insert member 68 and defines a central opening 80. A wave spring member 82 is also seated on another annular internal shoulder 84 of the insert member 68 and is secured in position by the lower surface of the support washer member 76.

A pivot retainer member 86 defines an enlarged circular retainer head 88 which is received in close fitting relation within the circular opening of the circular bushing insert member 68. The circular retainer head 88 defines a downwardly facing circular groove 90 within which received the upper end of an annular wave spring member 92. The lower end of the annular wave spring member is seated on an upwardly facing internal annular shoulder 91 that is defined within the annular bushing insert 68. The pivot retainer member 86 includes a downwardly extending retainer shank or shaft 94 having a lower threaded section 96 to which is threaded an adjustment nut 98.

A cam plate member 100 defines a non-circular opening 102 through which the downwardly extending retainer shank or shaft 94 of the retainer member extends. The shank of the retainer member 86 defines a non-circular section 95 that matches and is in registry with the non-circular opening of the cam plate member and prevents relative rotation but permits linear movement of the cam plate member relative to the retainer member. Thus, as the cam plate is rotated to its locked and unlocked positions, the retainer member 86 is also rotated within the circular opening of the bushing insert member 68. The cam plate defines a tapered cam surface 104 that establishes camming and locking engagement with an undercut tapered locking surface 106 of an accessory mounting rail 24 or 26 of a firearm, as shown in FIGS. 1 and 4. As the cam plate is rotated to its locked position, the tapered cam surface functions to wedge the cam plate tightly against the tapered surface 106 of the mount rail 24, thus drawing the opposite angulated surfaces 54 and 56 of the mount base into tight and secure locking engagement with the mount rail. The locator key 58, being engaged within a selected transverse slot of the mount rail, will prevent any movement of the mount base along the length of the mount rail. When locked to the mount rail in this fashion the mount base is secured against any movement relative to the mount rail and will thus serve as an efficient sight mount for a wide range of firearm sighting devices. Moreover, by simply rotating the locking cam plate to its unlocked position, the entire mount base and any sighting device or other accessory that is in assembly with the mount base can be easily removed from the mount rail. And, when the mount base is again assembled and locked with respect to its previous position on the mount rail, the sighting device will be positioned at its preset zero. Thus, a firearm user may transport a rifle and a sighting device separately to a site for use, quickly assemble the mount base to the accessory mount rail and expect to shoot a bullet precisely to a target, without any necessity for test shooting the firearm to establish a zero.

A circular flange 108 that is also defined by the cam plate member 100 about the pivot opening, projects upwardly into the lower circular opening 110 of the circular insert member 68 and ensures stabilization of the cam plate member during its rotation. A locking lever member 112 is formed integrally with the cam plate or is attached to it in any suitable fashion. A user of the firearm will apply manual force to the locking lever to rotate the cam plate to its locked and unlocked positions with respect to the accessory mount rail 24. In FIG. 4 the cam plate 100 is shown in its locked position, with its tapered cam surface 104 positioned in force transmitting locking engagement with the undercut tapered locking surface 106 of the accessory mounting rail 24. When the cam plate 100 is rotated to its unlocked position by manual rotation of the locking lever member 112 the tapered cam surface 104 will be moved to a position that is clear of the undercut mounting rail surface 106, thereby permitting the mount base, and any accessory device that is secured to it, to be removed from the mounting rail 24.

As mentioned above, the cam plate member 100 defines an upper planar surface 101 that engages the lower annular end surface 72 of the bushing insert member 68. Since the lower annular end surface 72 projects downwardly, slightly below the level of the planar bottom surface 74 of the platform structure 60 or 62, the upper surface of the cam plate member will be located in slightly spaced relation with the bottom planar surface 74, thus ensuring that no binding condition can be developed that will retard manual rotation movement of the cam plate member. Even though the retainer and adjustment nut 98 is rotated to tighten the position of the cam plate member relative to the bushing insert member, the upper surface 101 of the cam plate member will remain in spaced relation with the lower planar surface 74 of the platform structure 60 or 62.

With the locking lever in its locked position a lever retention member 114, being mounted to the mount base structure 46 for linear movement, is moved forwardly or to the left as shown in FIG. 5 to a position capturing the locking lever 112 within a lever retention recess 116, thus preventing the lever from being rotationally moved from its locking position.

In view of the foregoing it is evident that the present invention is one well adapted to attain all of the objects and features hereinabove set forth, together with other objects and features which are inherent in the apparatus disclosed herein.

As will be readily apparent to those skilled in the art, the present invention may easily be produced in other specific forms without departing from its spirit or essential characteristics. The present embodiment is, therefore, to be considered as merely illustrative and not restrictive, the scope of the invention being indicated by the claims rather than the foregoing description, and all changes which come within the meaning and range of equivalence of the claims are therefore intended to be embraced therein.

Claims

1. An adjustable accessory mounting mechanism, comprising:

an accessory mount rail having clamp surfaces;

a mount base member having a clamp structure disposed for retaining engagement with said clamp surfaces;

a clamp support structure being defined by said mount base member having upper and lower surfaces and defining a retainer opening;

a clamp member having a clamping portion disposed for clamping engagement with a clamp surface of said accessory mount rail and being moveable to a locking position securing said mount base member to said mount rail and to an unlocked position permitting removal of said mount base from said mount rail;

a clamp retainer member extending through said retainer opening and pivotally supporting said clamp member for locking and unlocking movement; and

an adjustment member having adjusting engagement with said clamp retainer member and having positioning engagement with said clamp member, said adjustment member being located below said lower surface of said clamp support structure.

2. The adjustable accessory mounting mechanism of claim 1, comprising:

said clamp member having rotary movement relative to said clamp support structure and having upper and lower clamp surfaces and defining an elongate tapered cam surface establishing camming relationship with a clamp surface of said accessory mount rail;

said clamp retainer member being a retainer screw having a lower threaded end; and

said adjustment member being a retainer nut being threaded to said lower threaded end of said clamp retainer member and having position controlling engagement with said lower clamp surface of said clamp member.

3. The adjustable accessory mounting mechanism of claim 1, comprising:

said clamp retainer member being a retainer screw having a shaft portion of non-circular configuration; and

said clamp member having a retainer screw aperture of non-circular internal configuration and establishing a non-rotatable and linearly moveable relation with said non-circular shaft portion of said clamp retainer member.

4. The adjustable accessory mounting mechanism of claim 1, comprising:

an actuating lever extending from said clamp member and being manually rotatable for imparting rotary locking and unlocking movement to said clamp member.

5. The adjustable accessory mounting mechanism of claim 4, comprising:

a lock member being mounted to said mount base member and having an actuating lever locking position engaging said actuating lever when said clamp member is located at said locked position thereof and preventing unlocking rotation of said actuating lever, said lock member having an actuating lever release position permitting manual rotation of said actuating lever and said clamp member from said locking position.

6. The adjustable accessory mounting mechanism of claim 1, comprising:

said clamp support structure being a clamp support platform having upper and lower platform surfaces;

an annular bushing insert being located within said retainer opening and having a lower end projecting downwardly beyond said lower platform surface; and

said clamp member engaging said lower end of said annular bushing insert and having spaced relation with said lower platform surface.

7. The adjustable accessory mounting mechanism of claim 1, comprising:

a spring member being located within said retainer opening and having force transmitting engagement with said clamp retainer member and said clamp member and maintaining said clamp member in engagement with said adjustment member.

8. The adjustable accessory mounting mechanism of claim 1, comprising:

an upwardly facing annular support shoulder being defined within said retainer opening of said clamp support structure; and

an annular bushing insert being located within said retainer opening and having positioning engagement with said upwardly facing annular support shoulder.

9. The adjustable accessory mounting mechanism of claim 1, comprising:

an annular bushing insert being located within said retainer opening and having a circular recess therein;

said clamp retainer member being a retainer screw having a head portion located within said circular recess of said annular bushing insert and defining a downwardly facing annular spring retainer groove;

an annular spring member having an upper end portion seated within said downwardly facing annular spring retainer groove and having a lower end portion disposed in force transmitting relation with said clamp member.

10. The adjustable accessory mounting mechanism of claim 1, comprising:

an insert member being located within said retainer opening and defining a circular rim and a retainer receptacle;

said clamp retainer member being a retainer screw having a screw head portion located within said retainer receptacle; and

said screw head portion and said circular rim of said insert member being substantially positioned in alignment and being in substantial alignment with said upper surface of said mount base member, thus providing said mount base with a substantially unobstructed upper surface and minimizing the potential for inadvertently catching the mount base on brush and other field debris during handling in the field.

11. An adjustable accessory mounting mechanism, comprising:

an accessory mount rail having angulated clamp surfaces;

a mount base member having internal angulated clamp surface structure disposed for retaining engagement with said clamp surfaces of said accessory mount rail;

a clamp support structure being defined by said mount base member having upper and lower surfaces and defining a retainer opening;

a rotary clamp plate member having a tapered cam surface clamping portion disposed for camming engagement with a tapered clamp surface of said accessory mount rail and being rotatably moveable to a locking position securing said mount base member to said mount rail and to an unlocked position permitting removal of said mount base from said mount rail;

a clamp retainer screw member extending through said retainer opening and supporting said rotary clamp plate member for rotary locking and unlocking movement; and

an adjustment nut member being threaded to said clamp retainer member and having positioning engagement with said clamp plate member, said adjustment nut member and a lower end portion of said clamp retainer screw being located below said lower surface of said clamp support structure.

12. The adjustable accessory mounting mechanism of claim 11, comprising:

said rotary clamp plate member having rotary movement relative to said clamp support structure and having upper and lower clamp surfaces and defining an elongate tapered cam surface at its periphery establishing camming relationship with a tapered clamp surface of said accessory mount rail;

said clamp retainer member being a retainer screw having a lower threaded end and having a shaft portion of non-circular configuration;

said clamp member having a retainer screw aperture of non-circular internal configuration and establishing a non-rotatable and linearly moveable relation with said non-circular shaft portion of said clamp retainer member; and

said adjustment member being a retainer nut being threaded to said lower threaded end of said clamp retainer member and having position controlling engagement with said lower clamp surface of said clamp screw.

13. The adjustable accessory mounting mechanism of claim 11, comprising:

an actuating lever extending from said clamp member and being manually rotatable for imparting rotary locking and unlocking movement to said clamp member.

14. The adjustable accessory mounting mechanism of claim 13, comprising:

a lock member being mounted to said mount base member and having an actuating lever locking position engaging said actuating lever when said clamp member is located at said locked position thereof and preventing unlocking rotation of said actuating lever, said lock member having an actuating lever release position permitting manual rotation of said actuating lever and said clamp member from said locking position.

15. The adjustable accessory mounting mechanism of claim 11, comprising:

said clamp support structure being a clamp support platform having upper and lower platform surfaces;

an annular bushing insert being located within said retainer opening and having a lower end projecting downwardly beyond said lower platform surface, said annular bushing insert defining a circular insert rim and defining a retainer receptacle;

said clamp plate member engaging said lower end of said annular bushing insert and having spaced relation with said lower platform surface; and

a spring member being located within said retainer opening and having force transmitting engagement with said clamp retainer member and said clamp plate member and maintaining said clamp plate member in engagement with said adjustment nut member.

16. The adjustable accessory mounting mechanism of claim 11, comprising:

a spring member being located within said retainer opening and having force transmitting engagement with said clamp retainer member and said clamp member and maintaining said clamp member in engagement with said adjustment member.

17. The adjustable accessory mounting mechanism of claim 11, comprising:

an upwardly facing annular support shoulder being defined within said retainer opening of said clamp support structure; and

an annular bushing insert being located within said retainer opening and being seated on said upwardly facing annular support shoulder.

18. The adjustable accessory mounting mechanism of claim 11, comprising:

an annular bushing insert being located within said retainer opening and having a circular recess therein;

said clamp retainer member being a retainer screw having a head portion located within said circular recess of said annular bushing insert and defining a downwardly facing annular spring retainer groove;

an annular spring member having an upper end portion seated within said downwardly facing annular spring retainer groove and having a lower end portion disposed in force transmitting relation with said clamp member.

19. The adjustable accessory mounting mechanism of claim 11, comprising:

an insert member being located within said retainer opening and having a circular rim defining a retainer receptacle;

said clamp retainer member being a retainer screw having a screw head portion located within said retainer receptacle; and

said screw head portion and said circular rim of said insert member being substantially positioned in alignment and being in substantial alignment with said upper surface of said mount base member, thus providing said mount base with a substantially unobstructed upper surface and minimizing the potential for inadvertently catching the mount base on brush and other field debris during handling in the field.