8-40 tap drill size?

[Lefty Trigger]

What size (letter or number) drill is used for 8-40 tap? Repairing a damaged scope mount on my Mauser. I found my dad's old box full of tiny taps and dies and it's full of lettered and number drill bits.

 

[butchlambert]

A #33

 

[GenePoole]

According to Machinery's handbook, an 8-40 needs a #28 which is 0.1405. A 9/64 is close enough at 0.1406. I use a 4-flute 9/64 carbide end mill to drill out 6-48 holes.

 

[GenePoole]

A #33

#33 is for 6-40.

 

[butchlambert]

#33 is for 6-40.

Now you see why I'm getting cataract surgery on Wednesday. You are correct.

 

[JohnKielly]

I'm getting cataract surgery on Wednesday. Y

Good luck. If it's anywhere as good s mine, you'll love it.

 

[Preacher]

A # 29 is what you need for a 8x40 thread....