Galley plugs not fitting

[SuperBuickGuy]

A heads up

I just ran into this issue with the 350 I'm building - in talking to NAPA, it's becoming common. The galley and casting plugs are not necessary the right size - I had 2 plugs that were supposed to be 9/16 (.5625) - for the front oil passages - that were actually .5600 - needless to say, they didn't fit correctly.

[Barry Donovan]

is it plain npt expecting a tape?
"nptf" is the tight fit.

I am still cramming 16mm X 1.5 into holley pressure regulators.

[squirrel]

pretty sure those are the cup plugs, that a lot of guys tap the holes for pipe thread.

[BigAL]

pretty sure those are the cup plugs, that a lot of guys tap the holes for pipe thread.

That's what I was thinking.

[anotheridiot]

3/8-14 is a 37/64ths drill size, Divide by 4 and you have a little bigger 1/64th bigger than 9/16. Shouldnt even need to drill, just tap since pipe taps are tapered anyway.

Otherwise, you flatten the plug on a steel plate till it baloons out to fit.