Screw for contaminated pre-tapped holes

Claim 1

A locking screw having an elongated shank section with a central axis, said shank section having a roll formed thread with opposed flanks that comprise radially inner and outer portions, said inner portion having flanks each at a first angle to a line perpendicular to said axis and said outer portion having flanks at the thread crest and each outer portion flank being at a second angle to said line, said second angle being smaller than said first angle, and a tip section at which the screw is initially inserted into a pre-tapped hole in which the thread is contaminated by a coating thereon; characterized by a tapered entry portion intermediate said shank section and said tip section, said entry portion comprising a thread with a lobular cross-sectional shape having circumferentially spaced lobes separated by intermediate arcuate sides, said tapered entry portion thread having been roll formed from a screw blank having a central axis and a surface region, said region comprising a pair of generally planar surfaces forming an obtuse angle to each other and which intersect along a line that lies in a plane that is perpendicular to said central axis, said entry portion thread also being a continuation of thread in said shank section and having truncations, said truncations forming indentations radially inwardly from the thread crests and with radial outer crest portions of the indentations constituting elements for engaging the coating and providing progressive action means commencing at the smaller end of the tapered entry portion for clearing contaminating coating from said pre-tapped hole.