Collar and double ended studs have a round or hex shaped collar formed in the middle.  Collars may be undercut to allow for flush seating at assembly.  Different thread forms may be used on either end, including standard machine screw threads, thread cutting, thread forming for plastic or metal, or knurled.  Drive features may also be added to one end or both ends for ease of assembly.

Round Collar Machine Screw with Locating Pin

Round Collar Machine Screw Stud

Double Ended Round Collar Machine Screw

Double Ended Machine Screw Stud

Round Collar Dogpoint Machine Screw with Hi Low Thread Cutting Screw

Hex Collar Machine Screw

Double Ended Round Collar Machine Screw with Hex Recess

Double Ended Machine Screw Stud Full Body