A shoulder screw's unthreaded section has a bigger diameter than the threaded section. I'm looking for the "opposite" if you'll pardon the term.

What is the name of the screw type where the unthreaded section is just a tad smaller in diameter than the threaded section? The unthreaded section has the same O.D. as the screw at the "valley" of the thread.

  • I have seen this in some "self threading" screws, but I do not know if there is a technical name for it. Tapcon concrete screws are like that for a specific example.
    – JPhi1618
    Nov 18, 2019 at 18:46
  • Called a rolled thread instead of cut.
    – Solar Mike
    Nov 18, 2019 at 18:51
  • With a little more research, "Thread Forming" is the type of screw I was talking about, but still don't think thats a complete answer.
    – JPhi1618
    Nov 18, 2019 at 18:52
  • And often used for cylinder head bolts when dissimilar metals are involved.
    – Solar Mike
    Nov 18, 2019 at 18:53
  • 1
    Are we talking about machine screws or structural (wood thread) screws? They're probably named differently.
    – isherwood
    Nov 18, 2019 at 18:56

1 Answer 1


They are called captive screws or captive panel screws.

Socket head captive panel screw

  • there are captive screws of other designs, but this certainly would be the usual application for such a screw.
    – Jasen
    Nov 19, 2019 at 7:36

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