[brassbullets12]

I Have Misplaced My Info On Proper Tap Drill Size For 6-48 And 8-40, Coundn't Even Find It In My Machinist Handbook Thanks Darrell

[highorder]

edit

6-48 NS #31 drill (.120")

8-40 NS #28 drill (.1405")

2A class fits.

[Zeke/PA]

Here's an easily remembered formula.

Tap Drill Size = Major Diameter minus Thread Pitch.
Example : 5/16 x 18 UNC
1/18= .055" 5/16 = .312"
.312"-.055"= .257" ( "Letter "F" Drill)
Works on smaller sizes and Metrics too!
Zeke

[35 Whelen]

Just Google "tap drill sizes". You'll get all the info you need!
35W

[PTK]

Funny how the two most common scope/sight mounting screw sizes aren't used in the Machinist's Handbook or on Starrett's tap guide, isn't it?

[BWB]

They are both "specials", used only for the purposes indicated. Specials are usually not listed in the fine or coarse thread standard tables.

[wolf_from_wv]

6-48 takes #32
http://www.midwayusa.com/eproductpage.exe/showproduct?saleitemid=293476

8-40 takes #28
http://www.midwayusa.com/eproductpage.exe/showproduct?saleitemid=352438

[Clemson]

I use a #31 for 6-48.

Clemson

[highorder]

its all about thread engagement. at small sizes like these, a few thousandths make a big difference in fit. But, considering the permanence of a scope mount, a little loc-tite makes up for alot of tolerance.

[rsilvers]

They are not listed because they are not standard screws. Basically, whoever selected them in the first place made a very poor decision by not picking something that was used for other things.

[BBBBill]

The Brownell's catalog has a chart of tap and clearance drill sizes. Surely you must have one. :)

[jimmyraythomason]

6-48 takes #32
I use a #31 for 6-48.
I have used both and they work equally well.

[rsilvers]

http://tinyurl.com/yh53229