RST Engineering wrote:

I've been wrong before and I'll be wrong again, but as I learned it the
blunt head "B" screw is properly called a PK.

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Dear Jim,

If you're referring to PK's as temporary sheetmetal fasteners (as I
was), that is also my understanding. It is based on something my dad
said more than fifty years ago when I was sent to fetch a handful of
PK's and returned with regular sheetmetal screws. He said you never
used the pointed type on rivet holes because you were liable to scratch
the metal, "You never want to make a scratch any where near a rivet
hole." Or words to that effect.

But the definition was even easier to remember when he pointed out that
the PK's he needed were black and had fiber washers.

I was even allowed to insert a few dozens of them :-) "Just snug will
do it; just snug is fine."

Odd, the things we remember...

-R.S.Hoover