Abstract: An automatic valve clearance adjuster comprising an internally screw-threaded housing (1); an externally screw-threaded screw member (3) extending within the housing; the screw thread (4) of the screw member (3) having an external form which is complementary to the thread form of the internal thread (2) of the housing and fits therein with a predetermined axial clearance, the thread being trapezoidal in form, symmetrical in axial cross-section and exhibiting equal frictional resistance against movement in both axial directions; wherein the flank angles, helix angle and number of starts of the screw thread are selected to ensure that the screw member will rotate and advance axially out of the housing solely under the influence of an axial force on its end within the housing; and the emerging end (7) of the screw member is adapted to work in conjunction with an adjacent component to receive therefrom a frictional resistance to rotation.

Abstract: A screw having a head and a threaded shank and, in the head, a cruciform shaped recess comprising a central cavity and four grooves radiating from the central cavity at 90.degree. angular spacings, the bases of the grooves lying on a conical (or pyramidal) surface and wherein the included angle at the vertex of such cone (or pyramid) has a value within the range of 40.degree. - 45.degree., the preferred value being 40.degree..

Abstract: A self-drilling and self-tapping fastener, particularly suitable for use in relatively thick metal, which is made from a headed blank by a method including pressing into the cylindrical free end of the blank a pair of straight flutes, by dies which are closed together on a line which is acutely angled to both the leading and trailing walls of the flutes. The flutes are inclined in opposite directions relative to the screw axis and are positioned on opposite sides of the screw. The tip is machined off to a V-form, to provide a ridge angularly advanced about the axis of the screw relative to the cutting edges of the flutes. Further machining may remove metal from the sides of the drill point between the flutes to provide flats and the drill point may be turned to a circular cross-section to provide sharp well-supported cutting edges for improved wear resistance. The drill point may taper overall, being of smallest diameter adjacent the threaded fastener shank.