I am in search of a flat head machine screws with an 82 degree countersink that have 1/4-20 UNC thread, but have a countersunk head that is characteristic of a 5/16-18 standard screw. That is, I want a standard machine screw with an oversized head.

I have been trying to search for these, but no search term I've tried works. If such a fastener existed, what would it be called? Can anyone confirm that they do or do not exist commercially?

(I know of course that I could fabricate them, but for a number of reasons, that's not desirable.)

  • $\begingroup$ Have you tried talking to the usual bolt fabrication houses? I imagine that they might know if it is common or possible. $\endgroup$ – hazzey Jul 1 '15 at 1:39
  • $\begingroup$ Whitworth ......... $\endgroup$ – Russell McMahon Jul 1 '15 at 6:50
  • $\begingroup$ @hazzey Unfortunately I'm looking for a fairly small quantity, so I doubt any of them would be interested. $\endgroup$ – Ethan48 Jul 1 '15 at 14:37
  • $\begingroup$ @RussellMcMahon I'm not sure I understand, these are UNC threads, but if you know of such a screw with a compatible whitworth thread, that would work too. $\endgroup$ – Ethan48 Jul 1 '15 at 14:37
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    $\begingroup$ @Ethan48 That was a "maybe" suggestion. Historically Whitworth nuts were one head size larger than UNC/UNF. (Allows you to shear heads off small bolts without thinking :-.) There's no reason why they should extend this into your application, but they may. As you are no doubt aware , the different angle means that strength is lost when mixing UNC/ Whitworth so it's not viable in demanding applications. $\endgroup$ – Russell McMahon Jul 1 '15 at 14:46

I am not aware of anyone that makes such a beast nor have I seen one in the wild. What I have seen is head collars. collars are a tapered washer normally made of nylon but also available in metal that are designed to accommodate mismatched head taper. As they have no threads they can be used with multiple screws. Somewhere I have a box of them for #8 screws. Not what you were looking for but it might work. Also there are tapered lock washers.

  • $\begingroup$ Those collars might do the trick - as long as I could get them in the right materials. I tried searching google and my usual parts houses for 'screw head collar' and variants though, and all I found were shaft collars. Could there be another name for these parts? $\endgroup$ – Ethan48 Jul 1 '15 at 14:41
  • $\begingroup$ Probably, I might try tapered washer, but I never ordered them, just grabbed them from a bin. $\endgroup$ – hildred Jul 1 '15 at 14:48

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