Fixing rounded internal hex set screws?

[Donut]

I recently realized that the set screws for my scope turrets are rounding because of crappy Allen keys. I'm worried that if I replace them, they'll probably just round again, since they only use a 1.5mm hex hey.



So what I'm thinking is buying some new set screws and then slotting the head and using a precision screwdriver to tighten and loosen them, which brings up the questions -

Is that a viable fix?

What size/thread do these set screws look like?

[wildcard]

Get a new set of screws and some better hex keys. Then quit over torquing them!

[Donut]

Get a new set of screws and some better hex keys. Then quit over torquing them!

It has been impossible to properly torque them, let alone over torque them.

[wildcard]

Hmm.. you sure they don't use standard size hex keys instead of metric?

[tzahoy]

Looks like it could be a 4-40 which uses a 1/16" allen wrench which is just a tiny bit bigger than a 1.5mm.

Most firearms screws are not metric. But not all by any means.

[tzahoy]

Could also be a 4-48 or some other unusual finer pitch #4 English screw. Borrow a thread pitch gage to figure what it is, then order the right one from Brownells.

[BSlacker]

If it came from the factory with a 1.5mm hex key then most likely it is just a case of a poor quality hex key meets cheap set screw.
Small set screws are shallow. To make sure you are driving it from the bottom of the hole the end of the hex key must be flat. Here is a link to the ones I use and they have every size and shape. The tips are machined and hardened and fit perfect in the screw.

http://www.wihatools.com/200seri/263sermm.htm

You can find them at Grainger and most Frys. Don't use the ball end type on small set screws. Get the flat end.
Call or e-mail the maker they will most likely put some new ones in an envelope for you.

[motorhead]

you may be able to find torx head replacements. always get good allen wrenches for small stuff like this. key should fit tight with no wobble.
cutting slots=brain surgery.

[gadjeep]

When I have rounded out socket head screws I use a correspondingly sized torx key. Instead of placing the force on the flats (that are now rounded) it puts it into the corners. I have used it as a optomechanical tech for years and it works. Good luck.

[Donut]

I appreciate all the suggestions.

I think I'm going to find some replacements (apparently there's a fastenal on the way to work) and get a good, properly-sized driver, and then put the scope up for sale.

I've decided I want to upgrade to the new model (mainly for the Mil turrets and revolution counter, but the new single-bolt turret design is appealing, too.), but I can't sell this one in good conscience without fixing the issue.

[NeoWeird]

If I was a betting man, I'd bet my money that by your measurements and pictures that that particular set screw is a 3mm set screw with a 0.5 pitch. If a metric allen key was issued with it, I can all but guarantee it.

You have ~11.5 threads worth of thread (keep in mind that a full turn or so is taken off with the taper) across .2275". That comes out to JUST over .5mm pitch (like .001" per turn and keep in mind I ESTIMATED 11.5 turns) where as it would turn out to be around 50.5 TPI in standard and we don't usually go to half threads at that small of a size. While .113 IS the major of a 4-40/48 screw, most production and machine screws are turned undersized to prevent bind and galling when they are threaded into the matting part or bolt; .1135 on the other hand is less than .005" under 3mm. Given the fact that M3 0.5mm is a standard size and it came with a metric allen, I'd say that's you're best bet. Also .2275 is about .009" shy of 6mm. So the set screws you want (assuming black finish) are:

http://www.mcmaster.com/#93245a100/=2yqdsf

While you're at it, get one or two of these.

http://www.mcmaster.com/#57585a52/=2yqezp

$8.84 for 100 set screws and $6.25 for the proper driver. Just over $15 before shipping. Can't go wrong with that and McMaster will have it to you in less than 2 days usually. Hell, you can even throw in the left over bag and driver to the new buyer as replacement parts and upgrades.

ETA: I forgot to mention, you may have had trouble getting a good set because if they used a cup shaped tip on the set screw, it will want to depress into whatever it bottoms out on. This is GREAT if you want it to hold something like there is no tomorrow because it will essentially do a small staking into the matting part and it won't want to shift. This is BAD for precission work or if you are making slight adjustments from time to time as it will damage whatever it bottoms out on. The set screws I linked above have a flat head to prevent this and should give a good solid torque. Just use your judgment when you install the new bolts. If something starts to stick, don't force it.

[Donut]

Holy wow!

One problem is that it didn't come with ANY hex wrench. I had to go out and buy a set, and 1.5mm seems to be what fit.

At Fastenal today, the guy held it up to some kinda gauge and thought it might be 4-40. But like you, I counted the threads and it seems a little finer than 40tpi. I'd know for sure, except that they were out, and should have some tomorrow.

Definitely thank you for the lead on the M3 0.5mm possibility! I'll look into that at Fastenal tomorrow - Hopefully they have both. Worst case scenario, I buy the 4-40 tomorrow, if they fit - great, if not, I order the metric ones from McMaster.

[tzahoy]

Counting the threads it's certainly not a 4-40. Could very likely be 4-48 though.

[dfletcher]

Well this is definitely the "el cheapo" way of doing things, but if I have a stuck & rounded hex screw I usually get a torx head of just slightly larger size and tap it in - a T15 size usually works. The torx head has sharp edges that will engrave the corners of the hex screw head and hold.

I wouldn't routinely do that, but for a single screw or set of screw problem it's easy enough and works.

[Donut]

Neo, you are dead on with your analysis. I mentioned what you said to the guy at Fastenal today, and he went searching and found an M3 0.5mm gauge, and sure enough, that's what it was. Should have the screws on Monday. Thanks!