gvetter

What size drill bit do I use to drill a hole to be tapped for a 4-40 bolt? I have heard that I should use a .0888 bit but what is that in fractions of an inch (1/16?)

Thanks
George

foxx

My Feedback: (2)

George you need numbered drill bits, these are different size from standard drill bits. Harborfreight carries them. I need a set myself. If you look on your tap it will tell you what number bit you need.

Devo

The drill size for a 4-40 tap is .0890, which is a #43 drill.

Dsegal

The April issue of Model Airplane News gives a complete table taps and drill sizes required.

Dave Segal

dmheil

My Feedback: (5)

If you go to www.harborfreight.com you can get an entire drill set, fractions, numbers 1-60 and letter drills, along with a size chart for about $30.00. I have found this set very usefull. They're probably not the best drills in the world but for the price they're great. plus I olt drill motormounts and other balsa/lite ply stuff anyway.

MinnFlyer

My Feedback: (4)

In a pinch, you can use a 5/64 drill bit. The hole will be a little smaller than .089 (.078125 to be exact) so it's about 10 - thousandths undersize (or about the thickness of 5 human hairs) but if you just wiggle the drill a little that will be gone in no time. In fact, just drilling the hole usually makes it 5 thousandths oversize anyway. (Can you tell I used to be a machinist?)

Just go real easy with the tap, and if possible, use one with only 2 flutes

gvetter

Thanks for all of the responses, very helpful.

George