Abstract: A differential drawer slide for furniture parts that can be pulled out is provided. The differential drawer slide includes a body rail, a pull-out rail and a central rail. An adjusting part of the central rail is mounted so as to be adjustable between a release position, in which the central rail can be tilted with respect to the body rail and a stop surface of the central rail can be moved past the body rail, under a stop element of the body rail, and a blocked position. A lateral guide roller is rotatably mounted on the adjustment part (13) and interacts with a vertical web (3d) of the body rail. The central rail is shorter than the body rail and the pull-out rail.

Abstract: A guide assembly includes an annular guide body defining a cavity, and a plurality of roller assemblies mounted within the guide body. Each roller assembly includes an annular roller mounted onto a pin and arranged to rotate around the pin. The pins are arranged such that their axes define a ring around the interior of the guide body and the annular rollers arranged to protrude through respective openings in the guide body into the cavity. Each annular roller has a concave outer surface.

Abstract: A single-column conference table includes a base, a table top, and a lifting mechanism. The lifting mechanism includes an upright column having a bottom portion fixed to the base. A first accommodating chamber is defined inside the upright column. A lifting sleeve is provided in the first accommodating chamber. A second accommodating chamber is defined inside the lifting sleeve. The lifting sleeve is fixed to the table top. A driving unit is provided in the second accommodating chamber. The driving unit is a gas spring. A bottom of the gas spring is fixed to the base together with the upright column. A top of the gas spring is fixed to the support seat. The table top connected with the support seat can be lifted or lowered through the gas spring. The conference table is more stable and reliable during the lifting operation and can prevent the table top from rotating.

Abstract: A rolling device includes: an inner member that has a raceway face; an outer member that has a raceway face facing the raceway face; and rolling elements that are disposed between both raceway faces in a rollable manner, wherein at least one of the inner member and the outer member has a space formed therein. Further, a method for manufacturing a rolling device including an inner member that has a raceway face, an outer member that has a raceway face facing the raceway face, rolling elements that are disposed between both raceway faces in a rollable manner, and a space that is formed inside at least one of the inner member and the outer member by a 3D printer.

Abstract: A grooved linear bearing having a plurality of relatively rigid, laterally extending side plates and multiple sets of one or more circumferentially grooved bearings mounted laterally along and between adjacent side plates. One or more rod or tube corners or edges can penetrate mating peripherally grooved bearings, providing rotational stability for the rod mounted within the bearing; and inclusion of laterally spaced sets of such groove bearings (i.e., laterally along the linear bearing axis) can provide transverse (side-to-side) stability of the rod when slidably mounted within the linear bearing.

Abstract: A linear slide rail includes a rail structure and a slider structure. The rail structure has an elongated strip shape and defines a longitudinal axis direction, wherein the rail structure has two guide grooves respectively disposed at two opposite sides of the rail structure. The slider structure has a cooperating groove which is slidably sleeved on the rail structure. The slider structure includes a carrier assembly and two guide wheel seat assemblies. The two guide wheel seat assemblies are respectively disposed at two opposite sides of the carrier assembly, and the two guide wheel seat assemblies are respectively disposed corresponding to the two guide grooves at the two opposite sides of the rail structure. Each of the guide wheel seat assemblies includes a seat unit, a plurality of guide wheel units, a plurality of shaft units, a first lever unit, and a first adjusting unit.

Abstract: A buried plug has interference which is made to exert a load or stress less in a widthwise direction of the guide rail than in a lengthwise direction of the guide rail, thereby protect raceways on the guide rail against any deformation such as bulge. The buried plug has a mating zone to press fit into a counterbore of a bolt hole and a leading zone to guide the mating zone into the counterbore. Let assuming a definition that a direction perpendicular to a lengthwise direction of the guide rail is referred to a direction opposed to the raceway surface or the widthwise direction of the guide rail, the interference exerting a force on the counterbore in the widthwise direction is determined less than the interference exerting the force on the counterbore in the lengthwise direction of the guide rail.

Abstract: A tooth-bearing body having a first sequence (1) of teeth (2) and at least one second sequence (3) of teeth (4), wherein the teeth (2) of the first sequence (1), viewed in a rolling direction (5) of the tooth-bearing body, are arranged behind one another and the teeth (4) of the second sequence (3), viewed in the rolling direction (5) of the tooth-bearing body, are likewise arranged behind one another, and the first sequence (1) of teeth (2) and the second sequence (3) of teeth (4) are arranged in a transverse direction (6) orthogonal to the rolling direction (5), particularly exclusively next to one another, wherein the teeth (2) of the first sequence (1) are larger than the teeth (4) of the second sequence (3).

Abstract: A support base for securing a linear motion guide track in a defined location comprises an elongated support body having one or more receiving slots, each slot including inwardly extending deformable teeth-like protrusions that deform upon insertion of the guide track into the slot thereby firmly securing the guide track to the support base without the use of traditional fasteners.

Abstract: A roller bearing sub-assembly can include a first mounting portion, a second mounting portion spaced apart from the first mounting portion, a first roller disposed between the first and second mounting portions and straps wrapped partially around different portions of the first roller. The first mounting portion, second mounting portion, first roller and straps are configured such that the first and second mounting portions are moveable relative to each other along a selected direction for a distance that is approximately equal to a circumference of the first roller in opposite directions from a mid-stroke position. Linear roller bearing assemblies and methods of forming linear roller bearing assemblies are also disclosed, as are multi-cylinder Stirling engines and a thermal energy recovery system.

Abstract: A guide rail that includes a base rail having a channel therein and at least one finger extending from a portion of the channel. The guide rail further includes a race insert mounted against the at least one finger. In an embodiment of the invention, the race insert has a first and second raceway associated with the at least one finger extending from a portion of the channel. Further, the first and second raceways have different load transmission directions, wherein the load transmission directions of both the first and second raceways are oblique to the direction that the at least one finger extends from a portion of the channel.

Abstract: A slide rail device includes a guide rail, a slider slidable along the guide rail, and a pair of cylindrical roller train sets disposed at two opposite sides of the guide rail. Each cylindrical roller train set is disposed between the guide rail and the slider, and has a plurality of cylindrical rollers. Each cylindrical roller has a first roller surface portion and a second roller surface portion that is recessed relative to the first roller surface portion. The first roller surface portions of the cylindrical rollers are in rolling contact with the guide rail and the slider, and the second roller surface portions of the cylindrical rollers are free of contact with the guide rail and the slider.

Abstract: A connection structure of first and second linear motor type transport devices each having a base part, and a rail part set on the top surface of the base part is provided, including: a notch concave part formed in the top surfaces of the base parts with both devices connected; a reference positioning part serving as a reference position of lower edges on one side in the width direction of the rail parts; a bottom surface support part disposed in the notch concave part, and set between the bottom surface of the notch concave part and the bottom surfaces of the rail parts; and a pressing member interposed between the wall part of the notch concave part and lower edges on the other side of the rail parts, and urging the lower edges on the other side of the rail parts toward the reference positioning part, thereby linearly fixing the first and second linear motor type transport devices to be connected.

Abstract: A system for securing a linear motion guide track (1010) to a support extrusion (1030) comprises an elongated wedge (1040) having a protrusion configured for insertion in a slit in one side of the well of the support extrusion for positioning the wedge in the well, the wedge having deformable teeth on a side opposite the protrusion such that insertion of the guide track in the well deforms the teeth of the wedge thereby securely holding the guide track in the support extrusion.

Abstract: The present invention provides novel approaches to manufacturing and assembling linear motion slides that are quick and easy to install without requiring the use of fasteners. Additionally, the present invention discloses a novel track assembly apparatus that couples with standard linear motion support bases without the use of fasteners.

Abstract: An upper roller assembly for a sliding vehicle closure system includes a first bracket secured to a sliding vehicle closure. A ball-type roller is secured to the first bracket at a location spaced apart from the sliding vehicle closure for engaging and moving along an upper guide rail during opening and closing of the sliding vehicle closure. The ball-type roller is fixed in position relative to the sliding vehicle closure during opening and closing thereof. A second bracket is connected to first bracket. The second bracket is moveable relative to the sliding vehicle closure during opening and closing thereof. Guide rollers guide movement of the sliding vehicle closure during opening and closing thereof. The guide rollers are rotatably connected to the second bracket for engaging and moving along the upper guide rail during opening and closing of the sliding vehicle closure.

Abstract: Bolt-on clamp extrusions for fastening a track to support base extrusion for providing customers with a simple-to-assemble, customizable, reconfigurable, and user-friendly solution for reliable linear motion track assembly. A back-to-back track configuration provides a low-profile track assembly. Custom made base extrusions include deformable fingers disposed in the slot to ensure proper fit despite a variance in track size.

Abstract: Rigidity and precision of a motion guidance apparatus are increased by improving track rail shape. A track rail has at least two rolling member rolling grooves (RMRGs) on the upper surface and at least one RMRG on each side surface, the RMRGs extending in the longitudinal direction. When the RMRGs are taken along a cross-sectional plane perpendicular to the longitudinal direction of the track rail, and two imaginary lines extending vertically downward are drawn from ends of the respective grooves located on the outer sides among upper surface RMRGs, all the side surface RMRG are positioned in the rail but outside the corresponding one of the two imaginary lines, and at least portions of the upper surface and the side surfaces of the track rail, on which the RMRGs are formed, the portions being in the vicinity of the respective RMRGs, are formed with an inclination angle.

Abstract: A guide rail includes a base rail with at least one finger extending from a first portion of the base rail, and at least one finger extending from a second portion of the base rail. A race insert is mounted against the fingers. A first race way is associated with the at least one finger extending from the first portion of the base rail. A second race way is associated with the at least one finger extending from the second portion of the base rail. The first and second race ways have different load transmission directions. The load transmission direction of the first race way is non-parallel to the at least one finger extending from the first portion of the base rail. The load transmission direction of the second race way is non-parallel to the at least one finger extending from the second portion of the base rail.

Abstract: A linear motion guide unit is provided, which is capable of preventing the variation in the position of a roller cage assembly caused by sliding motions of the roller cage assembly between a first guide rail and a second guide rail, without reducing the number of rollers. The linear motion guide unit includes first and second guide rails having track portions formed concavedly to have a V-shaped section on the faces opposing each other; and a roller cage assembly disposed between the first and second guide rails and having a plurality of rollers located between the first and second guide rails and ring-shaped pinions adapted to surround the rollers.

Abstract: A method of making a bearing assembly and a bearing assembly is provided. The method includes the steps of extruding a support rail, providing a mounting surface on the support rail, mounting a bearing rail on the mounting surface and machining a bearing surface on the bearing rail. The bearing assembly includes an extruded support rail and a bearing rail. The bearing rail is of a harder material than the material of the support rail to which the bearing rail is mounted. The bearing rail further provides a machine polished linear contact.

Abstract: A slider for a motor vehicle seat including a stationary profile section extending in a longitudinal direction and comprising a substantially planar base plate and at least one side shoulder, said base plate having a substantially constant width and including an attachment area for receiving a head of a fastening screw, wherein the stationary profile section has a local deformation increasing the width of the base plate and narrowing the shoulder to the extent that the raceway of the stationary profile section is blocked; a movable profile section; roller elements rolling along a raceway extending longitudinally on the shoulder of the stationary profile section and retained in position relative to each other by cage.

Abstract: A manufacturing method for appropriately manufacturing an arc-shaped rail that is C-shaped in cross section includes: a first process of forming one side wall 313 and one of circumferential wall portions 312 by bending a ring R of a thin metal plate by spinning, the circumferential wall portions 312 being portions on both sides of a width direction of the inner circumferential wall or the outer circumferential wall divided by a slit 314; a second process of forming the other side wall 313 and the other circumferential wall portion 312 by spinning using a plurality of cores 41 to 43 so as to envelop the cores 41 to 43, the cores 41 to 43 being obtained by dividing a core in a width direction to not more than a width of the slit 314; and a third process of separately extracting the cores 41 to 43 from the slit 314.

Abstract: A guide rail and method of forming a guide rail is provided. The guide rail includes a base rail having a groove with a plurality of fingers formed therein and a race insert mounted in the groove. The race insert has at least two different load directions. The fingers extend generally non-parallel to the different load directions. The fingers are preferably deformed into a state of bending.

Abstract: A ball retainer chain includes a flat belt with axially arranged holes defined thereon. A separating portion is disposed between every two holes; upper/lower spacers combine with the separating portion. The surface between the separating portion and the adjacent hole is formed by a smooth surface. Partial spacer is formed by a spherical surface that smoothly connected to the hole surface. The spherical surfaces interlacedly arranged at a right side a left side include an opening with a vertical direction and a lateral directions corresponding to the flat belt, so that a mold pair reliant on a slantwise opening and closing manner would complete an injection molding. A smooth cylindrical form at two ends of the flat belt connects to an indentation at an inner or a mold surface of the flat belt. Thereby, while applying the belt to a linear guide apparatus, the cylindrical form could adjustably bend inward or outward for achieving a fluent traveling.

Abstract: An assembly for coupling a track with a base extrusion via a support extrusion and a wedge assembly. A double-edged support extrusion for coupling a track with a guide wheel via a wedge assembly according to some embodiments of the invention. Methods for assembling an assembly for coupling a track with a base extrusion via a support extrusion and a wedge assembly and a double-edged support extrusion for coupling a track with a guide wheel via a wedge assembly.

Abstract: A bearing support ring includes a plurality of contact pads radially protruding from inner and outer circumferential surfaces of the ring. Flexible portions of the ring are defined between the contact pads and have a radial thickness less than that of the ring at the contact pads, such as to permit elastic deflection of the ring in a radial direction between the contact pads. Openings sized to permit unrestricted oil flow are provided, such as within the flexible portions of the ring.

Abstract: The invention relates to a linear guiding rail for a linear guiding system, comprising at least one guiding wagon being movable along the linear guiding rail by means of unrolling members, characterized in that at least one coolant groove extending at least along a partial length of the linear guiding rail is formed in the region of the linear guiding rail.

Abstract: A hydrostatic bearing for supporting horizontal and vertical forces, with a guide rail (2) and a support element (1) with a hydrostatic mounting on the guide rail, whereby the angle ? between the head side and the lateral guide surfaces (6, 8) of the guide section (3) is greater than or equal to 35 degrees and less than or equal to 75 degrees, and the angle ? between the mounting surface (7) and the lateral foot surface (9) of the mounting section (4) is greater than or equal to 10 degrees and less than or equal to 25 degrees.

Abstract: A roller guide for adjustable vehicle seats. The roller guide includes at least one guide rail which is at least partially open at the side and at least two rollers which roll in the guide rail and are connected to the vehicle seat via at least one axle. At least one of the rollers is shaped like a cone or a truncated cone. The cone surface can roll as the bearing surface of the roller moves along an inner wall of the guide rail. The inner wall being arranged at an angle with respect to the longitudinal axis of the axle.

Abstract: Bolt-on clamp extrusions for fastening a track to support base extrusion for providing customers with a simple-to-assemble, customizable, reconfigurable, and user-friendly solution for reliable linear motion track assembly. A back-to-back track configuration provides a low-profile track assembly. Custom made base extrusions include deformable fingers disposed in the slot to ensure proper fit despite a variance in track size.

Abstract: The present invention provides novel approaches to manufacturing and assembling linear motion slides that are quick and easy to install without requiring the use of fasteners. Additionally, the present invention discloses a novel track assembly apparatus that couples with standard linear motion support bases without the use of fasteners.

Abstract: A roller differential pull-out guidance for pulling out a pull-out furniture part from a furniture body includes a body rail securable on the furniture body, which rail includes a vertical base web, a pull-out rail securable on the pull-out furniture part, which rail includes a vertical base web, a horizontal flange connected with an upper margin of the base web and a side web extending downwardly from the horizontal flange at a spacing from the vertical base web of the pull-out rail. A center rail is located between the body rail and the pull-out rail and differentially running out between them, on which center rails are rotatably supported track rollers for the mutual displacement of the rails. On the body rail, a retraction unit is secured, which includes a spring-loaded tilt slide, which slide cooperates with an entrainer formed by a downwardly projecting section of the side web of the pull-out rail.

Abstract: An MID module with a plug-type connector for an optical fibre with an upper face, edge faces and a lower face, comprising an accommodating channel surrounded by walls for the accommodation of an optical fibre. Here the diameter of the accommodation channel essentially corresponds to that of the optical fibre. The MID module further comprises a semiconductor chip, which is arranged on a front face of the accommodating channel. The semiconductor chip comprises an optically active region, which is optically accessible from the accommodation channel. A slot is provided in the walls of the MID module for the accommodation of a locking element. A locking element, introducible into the slot, locks the fibre in the accommodating channel.

Abstract: A guide rail (1) of a linear guide, on which a guide carriage (2) can be mounted longitudinally displaceably, the guide rail (1) having an underside, by means of which it can be arranged on a mounting surface (3), and two opposite longitudinal sides which are provided with running tracks (8), rail parts (10) of the guide rail (1) which are arranged one behind the other being connected to one another by means of connecting elements (13, 21), a tension element (19a) being provided in order to brace the connected rail parts (10) with respect to one another.

Abstract: A method of making a bearing assembly and a bearing assembly is provided. The method includes the steps of extruding a support rail, providing a mounting surface on the support rail, mounting a bearing rail on the mounting surface and machining a bearing surface on the bearing rail. The bearing assembly includes an extruded support rail and a bearing rail. The bearing rail is of a harder material than the material of the support rail to which the bearing rail is mounted. The bearing rail further provides a machine polished linear contact.

Abstract: Slider for a motor vehicle seat including a stationary profile section extending in a longitudinal direction and comprising a substantially planar base plate and at least one side shoulder, said base plate having a substantially constant width and including an attachment area for receiving a head of a fastening screw, wherein the stationary profile section has a local deformation increasing the width of the base plate and narrowing the shoulder to the extent that the raceway of the stationary profile section is blocked; a movable profile section; roller elements rolling along a raceway extending longitudinally on the shoulder of the stationary profile section and retained in position relative to each other by cage

Abstract: A linear guide unit, in particular a gantry axis, that has an oblong guide support (14), is provided with two essentially parallel guide rails (24, 26) extending in the guide direction (F), but rotated in relation to each other around a rotation axis (V) parallel to the guide direction (F), each of which guide rails (24, 26) has at least one sliding carriage (36, 38) guided on it so that it can slide in the guide direction (F), the sliding carriages (36, 38) being connected to a sliding carriage assembly (36, 38) capable of moving as a unit in the guide direction (F). According to the present invention, the two guide rails (24, 26) rest essentially without moving play against at least two counterpart support surfaces (GF24, GF24L, GF24R, GF26, GF26L, GF26R) of the guide support (14) extending essentially in the guide direction (F), two of the counterpart support surfaces (GF24, GF24L, GF24R, GF26, GF26L, GF26R) enclosing a predetermined angle, preferably of at most 90°, between them.

Abstract: A guide section (1) for guiding a slide for a power tool along a longitudinal axis (A) with a separate axial toothed rack (3) for longitudinal advance of the slide having the toothed rack (3) arranged in an outwardly open receiving groove (4), with outwardly oriented toothing (5). The toothed rack (3) in cross-section forms at least two opposing sides (6a, 6b) laterally undercut relative to the toothing, in which the groove edges (7) of the receiving groove (4) are at least partially inserted and secured.

Abstract: A bearing arrangement (2) in a manual transmission for transferring torque between at least a first guide surface (14b) on a swivel element (14), which can swivel and which is fixed along the bearing relative to the manual transmission, and a second flat guide surface (19a), which can move in the longitudinal direction relative to the bearing (2) and which is supported with the swivel element (14) so that it can swivel at least in the bearing (2). The bearing holds a selector shaft (4) so that it can move in the longitudinal direction and so that it can also swivel, wherein the selector shaft (4) is provided with an adapter (19).

Abstract: A linear guide for transmitting a torque between a tubular housing, which is defined by a longitudinal axis and rotatable about the longitudinal axis, and a shaft, which is received in the housing and movable in the direction of the axis in relation to the housing, includes a bearing assembly received in the housing for support of the shaft and attached to the housing by swaging a housing portion. The bearing assembly has two bearing members and a set of rolling bodies disposed between the bearing members. One bearing member is constructed as bushing which is retained in the housing and defines a center axis which is oriented out-of-alignment with a normal upon a longitudinal shaft axis, and the other bearing member has a cup-shaped configuration to define a convex surface for support by a surface area of the shaft.

Abstract: A guide rail for a linear bearing has at least one rail element with a guideway for rolling bodies. The rail element is connected to a plastic body or borders the plastic body, with the plastic body forming the base body of the guide rail. To increase the precision of the guide rail, especially when used in an environment involving a wide temperature range, the rail element is connected to a metallic support frame which is surrounded at least partially by the material of the plastic body.

Abstract: A ball bearing rail assembly includes a first slide member (100), a second slide member (200), and a plurality of ball bearings (300) movably retained in the first slide member. The first slide member includes a plurality of spoon-like tabs (12), each tab forming a recessed portion (120) at a free end thereof. A plurality of slots (14) is defined in the first slide member, each slot having a generally oval end portion (140). The recessed portions of the tabs fittingly and resiliently press the ball bearings against the first slide member at the oval portions of the slots respectively. Each ball bearing is partially exposed out of the first slide member at a corresponding oval portion of the slot. The second slide member is slidably engaged with the exposed portions of the ball bearings. Thus the first slide member can be reliably moved relative to the second slide member.

Abstract: A linear motion guide device having a motion guide device capable of preventing thin and long-scaled support member and escape passage constituting member from being flexed and preventing an inner periphery guide section constituting member from being opened. Provided are Support members for preventing rolling members from coming off from loaded rolling member rolling passages when a movable block is removed from a track rail. Escape passage constituting members are provided constituting escape passages and the inner periphery guide section constituting members are provided constituting inner periphery guide section for direction changing of the rolling members are formed of resin so as to be respectively independent from the block body and from each other.

Abstract: A table apparatus with a linear guide device according to the present invention comprises a plurality of members constituting the linear guide device, other members to which the linear guide device is attached and screws for joining a predetermined combination of the members with each other, and screw holes for receiving the screws are formed to the members comprising the combination, and a gas vent hole in communication with a gap formed between the screw and the screw hole by receiving the screw in the screw hole, and the gas vent hole is perforated through the member constituting the table apparatus. When the table apparatus is put under evacuated or depressurized circumstances, remaining air in the gap formed between the screw and the screw hole can be discharged through the gas vent hole in a short period of time, a table apparatus suitable to be used under evacuated or depressurized circumstances can be provided.

Abstract: An angle &thgr;, which is formed by an axis of a horizontal roller rotatably attached to a slider and an axis of an inclined roller, is about 60°, and a load-bearing capacity of the horizontal roller is about a half of that of the inclined roller. Accordingly, the load resistance is substantially constant in four directions, i.e., in upward, downward, rightward, and leftward directions irrespective of attachment posture.

Abstract: In order to improve a slide system for machine tools, comprising a base member, at least one guide rail which is held on the base member and extends in a longitudinal direction and a slide guided on the guide rail with at least one guide carriage, in such a manner that the guide rails can be mounted with as great a precision as possible and as easily as possible it is suggested that the guide rail have a guiding area and a base area, that for the connection between the base area and the base member one of the two has a receiving means extending transversely to the longitudinal direction of the guide rail and the other has an insert member insertable into the receiving means, this insert member being inserted into the receiving means in a direction transverse to the longitudinal direction of the guide rail, that a clamping element be provided which acts on the insert member in the sense of a secure fit in the receiving means and that the insert member be fixed in a form-locking manner by the receiving means an

Abstract: The invention relates to a device that is provided with a C-arm 7 for carrying medical devices 5, 6, which C-arm is adjustably attached to a carrier 4. The carrier is provided with a bearing block 11 that is provided with at least one row of roller elements 8 on both sides. The C-arm is constructed so as to be hollow and is provided on both sides with at least two oppositely situated running surfaces 15, 16 for the roller elements. The device is characterized in that a plurality of roller elements of one row is interconnected by means of an interconnecting member 9. The invention also relates to a bearing block of the described kind that forms part of the device in accordance with the invention.

Abstract: A linear guide rail has: a rail body, straight-line ball rolling grooves being formed in surfaces of the rail body by form rolling, wherein curved corners are formed at joint portions between the surfaces of the rail body and the ball rolling grooves, the curved corners connecting smoothly the surface of the rail body to that of the ball rolling grooves.

Abstract: A track and trolley system for movable wall panels including a track having upper and lower flanges, the upper and lower flanges being horizontally and vertically displaced from each other and defining a channel therebetween, the upper and lower flanges each having a disc-supporting surface; a carrier shaft disposed between the flanges and adapted to engage the wall panel; and a trolley having upper and lower discs rotationally mounted on the shaft, the upper and lower discs each having a lower surface supported on the disc-supporting surfaces of the upper and lower flanges, respectively, and each of the upper and lower discs including an outer edge and a center, each of the lower surfaces sloping upwardly from the outer edge toward the center, each of the lower surfaces including a contact portion adjacent the outer edge and engaging the disc-supporting surface.