Safety set screw threads?

[AGDRetro]

I am looking to pick up a Dye Single Trigger frame and understand that the hole for the safety ball bearing set screw may be untapped. What is the thread used for this part? I have a suspicision it is a 4-40 but I'm unsure...

[flyingpootang]

I am looking to pick up a Dye Single Trigger frame and understand that the hole for the safety ball bearing set screw may be untapped. What is the thread used for this part? I have a suspicision it is a 4-40 but I'm unsure...

It's a 4-?. I tried a tap, but it wouldn't go in easy. 4-40 is the most common size, so try it first, but don't force it.