THREAD GAUGE QUESTION

BROCKWOOD

H-M Supporter - Gold Member
H-M Supporter Gold Member
Joined
May 26, 2017
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Been wondering for a while now what the number beside the TPI number means. I borrowed this picture from an OxTool video, because it represents best what I'm talking about. It is a 4 TPI - .325. What does the .325 mean?

4.jpg
 
I think its the thread depth x2 (measuring both sides). But that's just looking at my machinery's handbook and rounding off a bit. So that's possibly wrong. Nice for lathe work. Might have to compare a couple more thread gauges and see if this holds up.
 
It does represent double depth. You'll see the same number on a fish tail.
 
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