It’s true – there is a 100 degree countersink (well, 99-101 degree) but it’s not exactly common. In 20yrs of working in engineering, including 5 years in the US, I’ve never used it.
Not impossible though, but I’d hazard a guess as more unlikely than the more common standard of 80-82 degrees for Ansi standard screws. If you get bored, google ANSI B18.6.3 for specifications of both types.
You can buy 100 deg countersink bits in the UK – but probably only from proper engineering suppliers – and they won’t be too cheap. Mind you, proper 82 and 90 (90-92 deg) ones aren’t either.
Bri
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