During my electrican days, we used screw heads like that to secure light
fixture covers in jail cells. They were the standard screw on jail rate
fixtures. Those fixtures used a welded frame with 1" thick lexan lenses.
James
I've also
seen some screw heads that have three tiny round holes, arranged
>in a triangular pattern.
I've never seen those or the tools to R/R them (and I have a BOX full of bits).
I'm guessing that they're proprietary to one company.
Joe
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