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Working with Countersinks
(Tech Tip #1)
I want to use your threaded standoff, Part Number 12040RSS???-12 for a panel thickness of 10 GA sheet steel. I don't want to swage it, and after flaring, the shank must be flush to under-flush.
How do I figure the shank length? The countersink will be 82 degrees.
We will assume you are countersinking to approx. 1/2 panel thickness - the recommended depth. Panel thickness in the drawing below is represented by T.
We start with known data, and then apply the formula below. 
10 GA = .1345 Nominal thickness (T)
Shank length is therefore: .067 + .088 which yields .155. To ensure that shank is flush to under-flush, reduce the .155 by .010, resulting in .145.
Your complete part number would be: 12040-R-SS-.145-12.
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