6-48 stripped screw


March 16, 2007, 11:01 PM
Alright, just need some opinions on the repair for this.

I was out shooting my newly built 308 (98 mauser action) (first attempt at building) The scope base came lose. After taking it apart the front 2 screw holes are stripped (i am going to try to chase them out to make sure). If they will no longer hold the screw tight what should i do?.

I was going to retap for a 8-40 screw, should i do it for all 3 holes? or just the front 2 that are giving me problems?

Also what tap should i get, the bottom tap,plug tap, or taper tap?

and I have never used a 8-40 screw before so i am unsure of the size difference, but will i need to redrill the hole from the 6-48 or can i just retap it?

the 8-40 screw/tap requires the #28 drill bit correct?

Also last question, Is there a bushing available for both the drill bit and tap for the B-square jig? I am having no luck finding one.

Sorry for all of the newbie questions.

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March 16, 2007, 11:11 PM
If you go to the 8-40, you will have to redrill. One of the easiest solutions is to use an oversize 6-48 screw. It is made to fit the stripped out hole of a 6-48. It is more expensive than using the 8-40, but it is a lot easier and faster.


March 16, 2007, 11:16 PM
great, thanks for the reply. I might be ordering that tonight, I chased the threads on all 3. 2 seem to be ok but the front one has no threads left.

It's all my fault too, i forgot to loc-tight them :(

March 16, 2007, 11:36 PM
would the 8-40 be stronger and more secure for fastening the base than the 6-48?

Jim K
March 17, 2007, 10:32 AM
I recommend using 8x40 across the board, but especially with a heavy recoiling rifle or heavy scope. Yes, the tap drill is #28, but you should not need to use a jig since the holes are already located and the drill will follow the old hole using just the drill press. Most of the jigs come with the bushing for 6x48, but Brownells sells other sizes separately for around $7.00.

FWIW, I don't like having different screw sizes in a mount. There is just too much confusion when you remove and replace the mount and try to figure which screw goes in which hole.


March 17, 2007, 02:43 PM
thanks jim.
I was thinking about just going to the larger screw just to make me feel better about it. I don't really have a heavy scope, its a bushnell banner 6-18x50 and its not a high recoil rifle as it is a 308 win.

Also, I was thinking about bedding my base. what if any benifit does this offer?

Jim K
March 17, 2007, 05:15 PM
I may get dissenters, but I see no advantage to bedding a base. Just make sure you have the right base and that it will snug down right. And BTW, I do NOT recommend using loctite. Some people just have to slather it on everything in sight, but you might just want to take off that base someday. Also, FWIW, I don't like Allen screws; IME, they will tear out under pressure. There were some Torx screws around, and they are fine, but I prefer slot screws over Allen.


March 17, 2007, 06:00 PM
I'm not a big fan of allen's either. i think when i order my 8-40 tap and drill i'll get some slot screws.

what is the tourque specs for tightening a 8-40 screw? I am always afraid to over tighten so i think i don't go tight enough most of the time.

March 17, 2007, 11:53 PM
I use helicoils. I just found out about them a few months ago from the machinist in our department. They kick butt! I use them in aluminum, where frequently used holes strip easily.


I use them on 6-32. Not sure if they make them for 6-48. You could always go to the coarser thread, like the 6-32 or 6-40, which they certainly have.

March 18, 2007, 12:06 AM
i didn't know they even made helicoils that small. So i never looked into them. But i think i might just order the 8-40 tap/drill set and redo them all to that size.

March 18, 2007, 12:47 AM
While I don't know Jim personally, after reading many of his posts, he is a very intelligent man who knows his stuff. If he recommends using 8-40s, that's exactly what I would do too.

March 18, 2007, 11:00 PM
You could probably get a 6-48 Helicoil kit,but......
it will be a special order item and rather expensive.

If it stripped out a 6-48 from recoil,I's also recomend going to 8-40's.

For what it's worth,I've found that I can buy common sizes Heli Coil kits at auto prts stores for far less than the catalog prices from machine tool venders.

March 19, 2007, 04:26 PM
I placed my order last night for the new tap,drill bit, and screws. It was shipped just a little while ago. I also go my marine-tex today via the big brown truck :) plenty of projects this week to keep the days going fast.

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