Thread: Tap Drill for 4-40 Roll Form Tap

What tap drill for 4-40 roll tap in brass? What cutting or lube oil? Anything thing else?

Use a #39

This is a good guide for tap drill sizes for both cut and roll (form) taps

http://www.cncbasics.com/info/TapDrill.pdf

Side Note: I really like form taps. I used to be kind of hesitant to use them, but now I use them almost exclusively for tapping 1/4-20 and smaller. And as a side question, does anyone have a reason NOT to use them? I've tried them out in all types of steel (<38Rc), SS, and of course all the softer stuff and the only time I've broken one is after it's been completely worn.

What type cutting oil or lube?