Abstract: An improvement of an output shaft of a booster is disclosed. An output shaft 23 is formed by a push rod 24 and an adjusting screw 25. The push rod 24 is formed with an axial bore 26 in its distal end, the axial bore including a portion 26b of a reduced diameter which is less than an outer diameter of a threaded section 25C of the adjusting screw. The threaded portion is formed as a self-tapping screw. The adjusting screw includes a guide 25D at a location which is initially inserted into the axial bore before the threaded portion is inserted into the threaded portion. The guide comprises a plurality of annular projections 27 having an outer diameter which is substantially equal to the inner diameter of the axial bore. With this construction, when the guide 25D is fitted into the portion 26b of the axial bore 26 which has a reduced diameter, the axis of the adjusting screw 25 may be brought into alignment with the axis of the push rode 24.

Abstract: Structure for screwing on sheet metal an object having a fitting hole comprises sheet metal having a prepared hole formed therein in the shape of a saucer and also having a saucer-shaped lip which has a thickness equal to the thickness of the sheet metal and defines the prepared hole, and a screw composed of a screwhead, a shank depending from the screwhead, external threads formed around the shank and a substantially conical tip. The screw is passed through the fitting hole in the object and driven into the prepared hole in the sheet metal while catching the leading end of the saucer-shaped lip between the adjacent external threads.

Abstract: A method of making a screw for forming internal threads in a hole in a work formed from a blank having a shank portion and a frusto-conical shaft portion. Three flat portions extending parallel with the axis of the blank are formed on the shank. A length of the end portion of the frusto-conical shaft portion is left as right circular. A delta formed region is formed on the head end of each flat portion, and has a peripherally arcular convex surface and tapers to the flat portion. By thread rolling all but the shaft end portion, spoon-like recesses are formed at the crest of the threads passing on the flat portion to form inducing male threads. The depth of the spoon-like recesses sequentially decrease on the delta formed region to produce transient torque increasing characteristics.