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8-40

s.guns.gun Member Posts: 3,245
edited September 2001 in Ask the Experts
Checking my Mount Screws and they look as though they are #8-40 T.P.I.They came with a Weaver Mount,but I can't find that size in my book'sMajor Diam.=.162Checked threads with Thread Gage. (40)Can I buy a tap for this and what size should I drill ?

Comments

  • Der GebirgsjagerDer Gebirgsjager Member Posts: 1,685 ✭✭✭✭✭
    edited November -1
    8-40 is a fairly common size screw for this purpose. You will need a No. 28 drill bit. Of course, nothing says you have to use those screws. 6-48 is a more popular size, No. 31 drill bit. You can probably find an 8-40 tap at your local hardware store, but the 6-48 will probably have to be purchased from Brownells, 515-623-4000, about $1.50 each in lots of 5.
  • M.OpaliskiM.Opaliski Member Posts: 244 ✭✭✭
    edited November -1
    Good info from Der Gebirgsjager, he's on the money with the advice given. Now, if you want to stick with the 8-40 drop me an email and I'll send you a tap ... have a few lying around one of my toolboxes somewhere, your call.
    Support your RKBA ... MatthewNRA Life MemberTalk Radio * [email protected] TheFirearmsEnthusiast
  • Guns & GlassGuns & Glass Member Posts: 864 ✭✭✭✭
    edited November -1
    Weaver did/does use 8-40's with many mounts because the mount is usually aluminum, and the larger head (especially if tapered) provides alot more resistance to 'hole pull-out'. 8-40's are alot stronger than 6-48's, and in magnum cals., lightweight cannons, larger/longer/heavier scopes which are mounted higher are often times used. Besides the screw head hole/slot is larger allowing a larger tool head, ie..#10 vs #15 Torx.However, as Mr's "D&O" previously posted #6-48 is more often than not more than strong enough.Suggest you also buy or make a 'bottom tap' for the front hole. A broken tap is a royal pain in the "tapper's rear hole".
    Happy Bullet Holes!
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