PanoTools:
re: "imperial screws"
Chuck Norcutt 2004-Nov-12 22:42:43
If you are speaking of normal camera/tripod mounting screws and nuts the
sizes that you require are S.A.E. (Society of Automotive Engineers) or
(same thing) UNC (UNified Coarse) sizes 3/8x16 and 1/4x20. That is; 3/8
inch diameter with 16 threads per inch and 1/4 inch diamter with 20
threads per inch (most common camera thread). There are also UNF
(UNified Fine) sizes which have a greater number of finer threads per
inch but these are not used for mounting cameras on tripods.
Someone earlier mentioned Whitworth threads. Whitworth was the British
system up until about 1960 before the British converted to metric.
There is some overlap with the SAE/Unified scheme but they are not
identical. In particular, a 1/2 inch SAE wrench is for a bolt or nut
with a 1/2 inch head. In the Whitworth system the 1/2 inch designation
meant the bolt diameter and not the head diameter. The head was assumed
to be of a larger and appropriate standard size for that bolt diameter
but wasn't necessarily marked on the wrench.
So, use SAE taps and dies and pay attention to the number of threads per
inch since this can vary whether the thread is considered "coarse" (used
on camera equipment) or "fine" (typically what's used on automobile or
other high strength bolts)
Chuck Norcutt
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