| 摘要 |
<p>BLANK FOR THE MANUFACTURE OF EXTRUDING AND TAPPING SCREW Disclosed is a screw blank used in the formation of an extruding and thread-forming screw fastener which includes a shank with an enlarged head at one extremity, The shank is comprised of a substantially cylindrical upper portion of a predetermined diameter adjacent the head of the blank and a lead portion formed at the extremity opposite the head. The largest diameter of the lead portion is less than the predetermined diameter of the upper shank portion, and an intermediate, transition shank portion between the lead and the upper shank portions includes a pair of dissimilar partially frustoconical tapering regions forming two opposing, peripheral segments of the transition portion located on either side of a plane extending longitudinally of the blank. A first of the two opposing peripheral segments merge with the upper shank portion along a juncture line lying on a plane transverse of the shank which is disposed at an acute angle downwardly relative to a plane extending perpendicularly to the longitudinal axis of the blank. The lowermost region of the first of the two segments extends downwardly on the shank a distance from the head which is greater than the extent of the lowermost region of the second of the two segments. The angle of taper of at least the first of the two periphery segments relative to the longitudinal axis of the blank is generally 6.degree., so that a single lobular region is created on a blank which facilitates the formation of a screw with a threadforming region which has a plurality of partial threads on the lobular region and an absence of threads on the opposing peripheral side of the screw which therefore minimizes the drive torque to apply a screw of this type.</p> |
