6-48, 8-40 Tap Drill Size ??


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brassbullets12
March 5, 2008, 12:26 AM
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

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highorder
March 5, 2008, 12:37 AM
edit

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

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

2A class fits.

Zeke/PA
March 5, 2008, 03:42 PM
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
March 6, 2008, 01:30 AM
Just Google "tap drill sizes". You'll get all the info you need!
35W

PTK
March 6, 2008, 10:07 AM
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
March 6, 2008, 06:04 PM
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
March 7, 2008, 01:22 AM
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
March 8, 2008, 04:08 PM
I use a #31 for 6-48.

Clemson

highorder
March 8, 2008, 04:36 PM
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
April 4, 2010, 06:55 PM
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
April 4, 2010, 08:49 PM
The Brownell's catalog has a chart of tap and clearance drill sizes. Surely you must have one. :)

jimmyraythomason
April 4, 2010, 09:53 PM
6-48 takes #32
I use a #31 for 6-48.
I have used both and they work equally well.

rsilvers
April 4, 2010, 11:22 PM
http://tinyurl.com/yh53229

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