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SoCalDep
04-10-2020, 11:05 PM
My department recently authorized the use of pistol-mounted optics and so far we have over sixty people who have completed the prerequisites and two-day class. By far the biggest failure we’ve seen involves stripping hex screw heads or shearing the screws. A small bit of background:

We authorize factory-configured optic-capable pistols (M&P CORE, Glock MOS, STI Duo, etc.) and the authorized optics at this time are the RMR type 2, Aimpoint ACRO P-1, and Sig Romeo1 Pro. No aftermarket slides and no direct milling. I’m personally a fan of direct milling but the supervisors could not be convinced. Hopefully one day.

In our training/use we’ve seen a few sheared factory screws (two on Glock MOSs and a couple on M&P Cores) and a few stripped hex heads.

So far I’ve been very successful with my work and training pistols, which include three M&P COREs with RMRs and an SRO, and a Glock 19MOS with an RMR. I have a Unity Tactical ATOM slide and that’s where this all started. The ATOM RMR plate takes a 5-40 x 3/8” screw which is too long for the Holosun 507C I borrowed and mounted on it as a loaner for a class. I ended up shortening the screws and it worked great for around 1,100 rounds in the class. I purchased a Holosun 508T and when mounting it one of the screw’s hex-heads stripped. I could probably run it as is but that screw really bugs me so I’m looking at replacements. Currently I am waiting the California COVID 10-day to whenever they get to it waiting period for a new Glock 45 and have an ACRO en route. I already picked up a Tango Down mount and I expect no issues with the included McMaster-Carr screws, but I also took advice from Wayne Dobbs that the McMaster-Carr screws are superior to factory, so I did a bunch of research and this is what I’ve found:

Mr. Dobbs recommends the McMaster-Carr M3x0.5 x 6mm screws (part # 94414A712) for the Aimpoint factory Glock MOS mount. These are the same dimensions as the factory MOS plate-to-slide screws for the MOS plates. The screws for the MOS cover plate (no optic) seem to be M3x0.5 x 8mm.

I looked into the Google black hole as well as C&H, Forward Control Design, and Battlewerx, and found more dimensions and screw lengths for different handguns and optics. Battlewerx does a great job of listing dimensions and at least based on their pictures seem to use YFS screws. They do seem to be a really great “easy-button” option for replacement screws, but I’m looking for a source where I can get a larger number to have on hand for students who have issues. I also want Torx heads not hex.

McMaster-Carr offers flat head Torx screws in stainless steel, alloy steel, and high-strength 18-8 stainless. The alloy steel seems the “strongest” so that’s what I’m thinking of ordering, but I have questions because I’m not an expert on metallurgy, screws, etc.

First, the dimensions I found for the various optic/pistol configurations:

6-32 x 3/8” - RMR to MOS plate
6-32 x 5/16” - Holosun 407/507/508C and T series to MOS plate (Not available from McMaster)
M4x0.7 x 15.8mm - DeltaPoint Pro to MOS plate
6-32 x 1/2” - RMR or Holosun to M&P CORE
5-40 x 5/16” - Holosun 508T and others to Unity ATOM (Not available - I’ll grind down 3/8” ones)

It seems the FCD OPF-G plate is the same as the Glock MOS, using the same screw dimensions for the RMR.
From other threads, the C&H plate does not work with either the Trijicon “Glock sealing plate kit” screws or the factory Trijicon RMR screws but the Battlewerx screws fit. I have no personal experience with that.

Now the questions:

I want to order McMaster-Carr screws in the above dimensions since they use Torx heads (actually Torx plus which must be better because it says “plus”) and they seem to meet “standards” whatever they are.

Since I’m ignorant to all the dimensional aspects of these McMaster screws (82 degree counter-sink angle, thread count, pitch, course thread, etc.), does anyone know if ordering them would work to replace the factory screws or is there the potential for them to not fit?

The high-strength stainless is WAY more expensive than the alloy steel, which is listed as having comparable strength. I’d like to have a large backstock, so I like the bulk price of the alloy steel but if it is significantly sub-par the the high-strength stainless I’ll go with the stainless since it’s kinda important.

Lastly, I’m operating on the assumption that these screws are better than the factory screws supplied with most optics - If this is not the case I’d rather bite the bullet for quality and get the screws straight from the optic or pistol manufacturer, but it seems to me that for many of them they are cheaper parts with very high markups. What do you all think of the quality of McMaster-Carr screws and would they be an “upgrade”?

I know there are all sorts of other aspects of installation to include thread-lock, torque specs, thread seal or torque seal, etc., but those are primarily dealt with in other threads so I figured I’d focus on the screws themselves here. I still need to research the Sig Romeo1 Pro and the P365XL/Romeo Zero, as well as some other optics we’re looking at testing, but I’m calling this a good start.

Any help or information would be greatly appreciated!

GyroF-16
04-10-2020, 11:14 PM
Paging OlongJohnson

He’s my hero for knowing about hardware and the materials science related to such things.

GJM
04-10-2020, 11:18 PM
I am looking forward to seeing this thread develop. I have a slide on the way back to Primary Machine right now, to drill out a screw that sheared on a DP Pro. I also have a CH Precision Weapons P10 plate on a Shadow 2, where the tip of a bit broke off in the too small screw head. They told me they send out 100 spare screws with law enforcement orders and recommend changing screws frequently, and any time the optic comes off.

TAZ
04-11-2020, 12:06 AM
Not Oleg, so take this with a grain of salt..

"I want to order McMaster-Carr screws in the above dimensions since they use Torx heads (actually Torx plus which must be better because it says “plus”) and they seem to meet “standards” whatever they are."

We aren't applying enough torque to these things to worry too much about Torx, Torx Plus or Hex. Id focus on the size and thread pitch and material you want and let those narrow options.

"Since I’m ignorant to all the dimensional aspects of these McMaster screws (82 degree counter-sink angle, thread count, pitch, course thread, etc.), does anyone know if ordering them would work to replace the factory screws or is there the potential for them to not fit?"

Counter sink angle is the angle of the V at the top of the hole. 82degrees is kind of a default. There are others, but 82 is generic so to say.
51720
Most of the screws on McMaster should match this.
51721

Thread count is the total number of threads on a screw or how many are engaged between the screw and hole.

Pitch is the spacing between peaks on a thread.
51722

Corse thread, fine thread are related to the pitch mostly.

6-32 is corse thread at 32 threads per inch while 6-40 is fine thread at 40 threads per inch

Threaded items are described with the nominal diameter followed by a pitch then a fit(no need worry about this for our use as its a general use)

6-32 => #6 nominal shank diameter (.138") with 32 threads per inch
M4x0.7 => 4mm diameter with a thread pitch of 0.7mm

Flat head screws (like the image) are measured from the top of the flat to the end of the screw. Others are measured from under the flat of the haead.

"The high-strength stainless is WAY more expensive than the alloy steel, which is listed as having comparable strength. I’d like to have a large backstock, so I like the bulk price of the alloy steel but if it is significantly sub-par the the high-strength stainless I’ll go with the stainless since it’s kinda important."

You shouldn't need the high strength alloy. Ive designed stuff that would give someone a serious bad say if it broke an haven't had to resort to using the $$$$ screws. Granted there are more than 2 screws. For the RDS use a standard SST screw will work. They should have a tensile strength in the 60-70 thousand PSI range. Plenty IMO for an RDS on a slide. If you're really worried about corrosion resistance 316SST will give you the best bet at decent $$.

"Lastly, I’m operating on the assumption that these screws are better than the factory screws supplied with most optics - If this is not the case I’d rather bite the bullet for quality and get the screws straight from the optic or pistol manufacturer, but it seems to me that for many of them they are cheaper parts with very high markups. What do you all think of the quality of McMaster-Carr screws and would they be an “upgrade”?"

Mcaster is a good source, but they do use Chicom items. Not sure if that matters to you. Ive used McMaster for decades as a source for prototype and low production items. Everything from generic screws to mission critical 316SST holding together little pressure vessels that get beat to hell and are in harsh environments. Ive not had issues with their parts.

Hope this helps.

OlongJohnson
04-11-2020, 12:11 AM
Hah! I had literally just brought up the McMaster site when the email landed in my inbox telling me I'd been mentioned. Guilty as charged... (In my defense, Tom_Jones has out-fastener-geeked me in the past.) ETA: Then I took so long typing this up that several others responded ahead of me.

Me and my astigmatic eyes haven't messed with pistol dots, so I don't have any personal experience with what holds one together reliably, but since the question is just about replacing/upgrading hardware, I don't think it's likely to be hard. This is probably just a long, wordy, over-written version of what Wayne was telling you.

I guess I didn't realize you might be asking about the thread sizes and what that means. TAZ covered the basic concepts.

The stainless screws are close enough in strength (130ksi) to the number-sized alloy steel screws (120ksi) that other aspects of the joint design and assembly will dominate. (The metric 12.9 alloy steel screws are actually stronger.) But the A286 stainless screws cost each what a box of 50 or 100 alloy steel screws costs. The only benefit of the stainless would be corrosion resistance, but since there should be oil added to the firearm fairly often, wiping a dab on the black oxide screws to keep them from rusting shouldn't be a problem. As he jumped in above, GJM has been working on this situation, and his conclusion is change the screws every time they are removed, I believe. (ETA - Hey, I got that right.) That argues for the cheap ones as well.

For the metric stuff, be sure to get the grade 12.9, not the zinc plated 8.8. Not only is the material stronger, the 12.9 screws also have a tighter class of thread fit, so they will more fully engage the female threads.

I would disagree with TAZ on the 60-70 KSI stainless screws. IME, normal 18-8 stainless screws are usually formed for VERY loose thread fits and less than full thread forms (rounded tips), so you don't get the full engagement that you do with 10.9 or 12.9 alloy steel screws. With the tiny threads you're dealing with, that could make a difference.

The 82- vs 90-degree head should take care of itself, as 82 is typical for SAE/number-sized and 90 is typical for metric. In an ideal world, the engineers would trace it all to ground (specifying the fastener standard to be used, and then actually referring to that standard when designing the rest), but sometimes the CAD monkeys who get assigned to draw stuff aren't that experienced or detail oriented. It's possible a designer spec'ed the hole with the wrong angle or the machine shop used the wrong countersink on a part and no one caught it, if they weren't fully up to speed on that stuff. But you're not going to be able to do anything about it anyway, so I wouldn't worry about it unless you just can't keep screws alive in something. Then it might be something to check. Hopefully, the companies we are talking about for optics are way above the level of dropping a ball that way.

I would just buy a box of screws in each of the sizes you think you need in alloy steel and don't worry about it.

Try to get torque specs for everything from the manufacturer, and get a good torque driver. I use a Wiha (https://www.wihatools.com/torquevario-10-50-in-lbs)that I found online for a good price years ago. Amazon (https://www.amazon.com/28502-TorqueVario-S-Torque-Screwdriver-Pound/dp/B002QV0FCY)is kinda expensive, but you may be able to find it elsewhere for less. One of the drivers sold specifically for the firearms market should be fine, too. Make sure you use quality bits for the torque driver. I would pick up sets of Bondhus L-wrenches in Torx (https://www.amazon.com/Bondhus-31832-L-wrenches-Length-T6-T25/dp/B000E7XJR0/) and and hex (https://www.amazon.com/Bondhus-22199-L-wrench-DoublePK-1-5-10mm/dp/B000E7VG5C/)(Amazon is usually a good place to buy them, but check McMaster since you're ordering) for breaking loose and removing old screws. They're also easier to use than the torque driver for initial installation of the new screws.

I normally use Loctite 222 (https://www.mcmaster.com/loctite-222) purple for scope screws. Remember that Loctite is basically glue. Glue doesn't stick well to oily surfaces. The screw and the hole it's going into must be degreased before assembly (solvent clean the oil out) for it to work correctly.

If manufacturers provide a tightening procedure, follow it. In the absence of that instruction, I'd treat it like anything else, where you tighten progressively, going in a cross pattern, to keep it all even as you go. Don't crank one down to final spec while the others are still loose or just barely making contact.

Can't think of anything else to add. Happy to answer any further questions.

SoCalDep
04-11-2020, 01:29 AM
Thank you all for your replies! I had learned a lot about screws from research and learned more from TAZ’s post.

OlongJohnson - Thank you so much! You gave me some confidence and Lots more stuff to look into.

Next dumb question...

Compared to McMaster-Carr, since we have very smart people here... are there better options out there? Like I mentioned in my first post, I’ve stripped hex screws and I’ve seen others do the same with less than 15 inch pounds on a torque wrench (yes, maybe not the best bits but still) so I’m very much more confident in Torx heads.

whomever
04-11-2020, 06:50 AM
Compared to McMaster-Carr, since we have very smart people here... are there better options out there? Like I mentioned in my first post, I’ve stripped hex screws and I’ve seen others do the same with less than 15 inch pounds on a torque wrench (yes, maybe not the best bits but still) so I’m very much more confident in Torx heads.

If the question is 'is McMaster a good vendor for this kind of stuff' I'd say 'generally yes'. I order from them frequently and the quality is usually good, they have good inventory, customer service, etc. They don't quote shipping when you order, but have never gouged me (which isn't to say shipping won't be expensive if you order a 4x8 sheet of something). They don't usually list the brand of what they are selling, although they will tell you if you call. In general, I've had good luck with them, and order fasteners like you are shopping for all the time.

For probably more $$$$ you could get 'name brand' fasteners like Camcar or Holo-Krome from Fastenal or zoro.com or where ever. Personally, I've been happy with what I get from McMaster.

(I'll note in passing: Brownells has kits of optics screws. I don't have an opinion on their metallurgy. I have one of their kits for the oddball sizes, but for something that is a standard size/pitch thet McM sells I'd go with McM).

Duke
04-11-2020, 08:22 AM
Tagged for interest

Grey
04-11-2020, 08:27 AM
I don't remember which screw is which (plate to slide / optic to plate) but here is what I was told to buy from MCC...

EDP: #82692
M3 - 0.5 x 6 MM
Torx Plus
Flat Head

EDP:34395
4-40 x 3/8
Torx Plus
Flat Head

mmc45414
04-11-2020, 08:32 AM
Compared to McMaster-Carr, since we have very smart people here... are there better options out there? Like I mentioned in my first post, I’ve stripped hex screws and I’ve seen others do the same with less than 15 inch pounds on a torque wrench (yes, maybe not the best bits but still) so I’m very much more confident in Torx heads.
McMaster-Carr is a fine company (I believe the are based here in Ohio, Go Bucks!) but one alternative I use is Fastenal (https://www.fastenal.com/home), not because of quality but because they will sell many items individually (I think M-C only sells full boxes of many of these small items). They only do this online, but will ship your online order to a store I think for no shipping charge (though during Coronacation, a term I just stole from PatMac, you probably want to pay the shipping).

I learned this when I lost the tiny stainless roll pin changing the front sight in my SP-101, I really didn't need a box of one hundred… :cool:

rca90gsx
04-11-2020, 08:34 AM
What Grey posted here is correct and should work for you with a C&H plate to RMR for a Glock Mos setup.
The M3-.5x6mm is the plate to the slide screw. The 4-40 x 3/8 screw is for rmr to the plate for the C&H Glock MOS setup I have seen.


I don't remember which screw is which (plate to slide / optic to plate) but here is what I was told to buy from MCC...

EDP: #82692
M3 - 0.5 x 6 MM
Torx Plus
Flat Head

EDP:34395
4-40 x 3/8
Torx Plus
Flat Head

rca90gsx
04-11-2020, 08:37 AM
One thing I would add is to use the Loctite activator as well. It sets up very quickly and solved a lot of screws loosening. Just a thought.

OlongJohnson
04-11-2020, 10:41 AM
Not a bad idea. Loctite is catalyzed by the ferrous materials and in the absence of oxygen. The tubes and bottles it comes in are actually permeable to oxygen (like the wraps on meat at the grocery store) to keep it from setting up in the tube. If you're screwing together less active materials, such as coated or stainless screws into anodized aluminum, the primer can be helpful.

Duke
04-22-2020, 06:45 PM
If anyone is interested

The M&p core requires the factory trijicon RMR screws to mount it.

They are 6-32 and .496 long on my micrometer.

I’ve ordered some titanium torx head units from agency. Not because I wanted to pay $6 per screw but because the agency guys were kind enough to measure their screws for me despite not guaranteeing fitment with anything besides their optic cut.