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Originally Posted by Don Hoey
I fell over this one when trying to modify a tripod head for a scope.
I always believed the thread to be Whitworth and cursed as I did not have a die. When I later made a sighting device the previous experience forgotten and needing to support the head in a vice, I rummaged for a screw to fit, job done. Only later, as the origional project is ongoing, did I check out that screw and cursed again.
Seeing this brought it all back and I have just rechecked......... 1/4 x 20 UNC. the 3/8 thread is 3/8 x 16 UNC.
Whitworth, BSF, UNC, UNF. The difference is in the thead angle. Whitworth and BSF 55deg. UNC and UNF 60deg. Metric is also 60deg.
Don
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Amazing, even googling got this wrong for me
