Got this one from my step-dad, who taught machine tool for 35+ years:

If you're going to drill and tap a hole, and you don't know what size tap drill the tap takes, just use the size of the tap - 1/ thread pitch per inch.

So, a 1/2-20 tap takes a 1/2 - 1/20, or .500 - .050 = .450 drill, which is just about 29/64.

Just thought someone might find that useful. He says he's used it for years, and it's never been off by more than a few thousandths that he can recall.

Good tip
Its like the V8 with the 4.00" bore stroke +2 thing

I'm lucky or lazy. My old Craftman drill press has a chart printed on the side of it.

I'm lucky or lazy. My old Craftman drill press has a chart printed on the side of it.

your lazy....:goodfinge

I have horrible memory, but I have this little green book called a machinist handbook. Its very handy and everyone should have one

I have one of those, too (12th edition, 1946 I think). This is a useful shortcut, though.

I have horrible memory, but I have this little green book called a machinist handbook. Its very handy and everyone should have one

I got the miniature 27th edition. Works fine if you have a magnifying glass, and a few minutes to find what exactly you are looking for. Just too much info in that book.

Drill charts are the shiznit.