Expanded – threaded – driven – headed – tool-deformed – or locked-thr – Externally threaded fastener element – e.g. – bolt – screw – etc. – Pilot end having means enhancing fastening or installation
Patent
1991-08-27
1992-06-09
Wilson, Neill R.
Expanded, threaded, driven, headed, tool-deformed, or locked-thr
Externally threaded fastener element, e.g., bolt, screw, etc.
Pilot end having means enhancing fastening or installation
411418, F16B 2500
Patent
active
051201720
ABSTRACT:
A tapping screw has a threaded shaft and a stepped drill bit portion including two or more drill portions having different diameters gradually decreasing toward the tip of the screw. The small-diameter drill portion has a larger drill angle than the large-diameter drill portion. The former firstly forms a starting hole and the latter expands it. Thus, less force is required to rotate the screw than a conventional tapping screw. Recesses are provided in the drill bit portion and have respective sides defined by cutting edges extending across only the portion of the thread closest to the tip of the tapping screw.
REFERENCES:
patent: 3507183 (1970-04-01), Thurston
patent: 3578762 (1971-05-01), Siebol et al.
patent: 3937120 (1976-02-01), Munse
patent: 4978350 (1990-12-01), Wagenknecht
Wakai & Co., Ltd.
Wilson Neill R.
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