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Re: Thread size

Posted by Pete Nelson on Sunday, 16 May 2010, at 12:45 p.m., in response to Thread size, posted by Ernie on Sunday, 16 May 2010, at 9:05 a.m.

Good morning Ernie,

Back in January of 2008 I had set myself a task of making a complete table of all of the threaded fasteners and their respective male thread sizes (as well as the female tapped holes in items like Lock Plates, Barrels, Tumblers, etc.), using my two 26-tpi tap-and-die combinations as a thread pitch gauge and measuring the crest diameter of the male threads using my Starrett digital micrometer. Admittedly, some of the sample fasteners I was using were not perfect, but I was able to find some relatively-decent ones and clean them up a bit.

For the slotless and the later slotted-head Rear Sight Attachment Screws screws I came up with 0.157"-26 (and that was based on an average of the crest diameters of 10 samples in my parts inventory). A known dealer (and Dick knows to whom I refer) had told me on several occasions that he "just uses a worn #8-32UNC-2A slotted head screw of nearly the correct length and then just runs it in until it stops (?)!". The nominal crest diameter of a #8UNC thread is 0.164" and of a #6UNC thread is 0.138". When I placed the threads if one of the "minty" Rear Sight Screws against the 0.157"-26 tpi threading tap, the "mesh" was just about perfect. So, without making this long dissertation even longer, I cast my vote for 0.157-26.

Best regards,



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