CZ OR plates screws

[dabljues]

Hi,

A couple of weeks ago I got myself a CZ P-10F OR. I decided to mount a Holosun 507 Comp on it.

I went out and bought the optic and I bought the adapter plate (RMR footprint for the Holosun) which came with two screws (a factory plate from CZ). I got all of my tools which were: T10 Wera bit and a torque screwdriver. Set the screw driver to 1.3Nm which is what CZ suggested on their YT video (and I saw the same reference on cz-parts.com). First screw - no problem, screwdriver clicked, easy. Second screw - something clicked. As it turns out it was the two "teeth" inside the torx screw head - they broke off.

Long story short, I wasn't able to unscrew this screw. It got so bad that I decided to go to a local gunsmith who charged me a fair amount of money to get that out. As I had my gun deposited to the gunsmith, I went out and searched for replacement screws. What I found, even from this forum: https://czfirearms.us/index.php?topic=116707.0 is that those screws are M3. And either 6mm or 8mm. I've seen those screws on some sites like IPSCstore but the delivery was overpriced + the wait time unbearable, at least for me.

What I ended up doing is I bought a pack of M3x6mm T10 screws (didn't find 8mm ones) and another pack of M3x8mm 2mm allen screws. I really wanted the torx ones, since I don't have a 2mm hex bit for my torque screwdriver. And torx beats hex any day. Anyway, the gunsmith calls me up and says the job is done. We talked about what could be the cause of me stripping the screw. We established that:

* I had the slide in a vise
* I used a quality T10 bit (Wera)
* I used a proper setting on the torque screwdriver

He told me that the issue was: the screws (provided with the plate) were too long. I've even provided him with a bunch of crappy Chinese ones with the same length and he said that those with addition to being bleepe, are too long. I've seen some YT videos of people mount an RMR plate to CZ P-10 and some of them were using short screws, some of them were using long ones.

In the meantime, before I bought the screws of the internet, I e-mailed the shop that sold me the plate and asked if they maybe had some replacement screws. As it turned out today - yes they do and they'll send me a pair free of charge. I'm kinda at a loss here. Should I wait for those replacement screws (which will probably be 8mm long) or should I use the screws I bought? (the 6mm ones) I'm just wondering if 6mm here is "enough" to hold the plate + the optic down. 6mm seems "a safer choice" since I would be able to torque down to a desired spec without worrying about the screw bottoming out, getting stuck on the slide while torquing and potentially getting stripped again. But I'm wondering if the 6mm thread is enough to hold everything safely. On the other hand, the replacement screws could be "better" than those that I bought in a pack (maybe these are hardened or something, those that I bought are A2 steel, so not hardened per se).

What do you think? Which ones should I use?

[tdogg]

From my recollection of mounting my dot you want to confirm the screw length in the plate prior to mounting on the slide.  Mount the dot on the plate and verify the screws do not protrude below the bottom of the plate.  If they do, then you would cut/grind them shorter.  Once you have the dot mount screws the correct length then you proceed on mounting the plate to the slide and dot to the plate.

I don't think your conclusion on what happened is correct.  The screws you had are junk, that is the conclusion I deduced.  If the screw was too long, it would have bottomed out on the slide and reached the 1.3nM of torque just as if it had been tightened normally (if the correct length).  The fact that the teeth on the torx snapped prior to 1.3nM means there was a defect in the screw head.

I'd also confirm you are getting the right screw.  The Holosun Comp comes with 6-32 screws, plus the Holosun has a 90Degree countersink apparently?  I don't know what the factory CZ plate thread pitch is but you most likely are correct with the M3. You might need to find the right screw or wait for replacements from the shop.

I'd use whatever screw you have and verify it's countersink and length prior to mounting the plate.  If the 6mm is too short then get an 8mm.  You want to have several threads engaged in the plate (ideally just shy of the bottom of the plate) for stability and security of the dot.  I don't know how many threads there are on the plate total?  The nice thing is that you can clearly see how many threads are engaged when checking screw length prior to mounting everything.

Cheers,
Toby

[dabljues]

Hey, sorry for the delayed response!

I'm not sure we understand each other here. The dot screws weren't the problem, I didn't even get to mounting the dot. The plate screws were the problem.

My nomenclature:

* plate screws - screws that secure the plate to the slide (the go into the slide)
* dot screws - screws that secure the dot to the plate (they go into the plate and stay on top of the slide)

So I couldn't check for protrusion because the problematic (for me then, at least) screws are going into the slide, not on top of it (like the red dot ones do).

Today I received the 8mm screws and mounted the plate and later the dot successfully, no problem. The dot screws were protruding beneath the plate a little bit (I screwed the dot onto the plate before mounting the plate to the slide to see how much they protrude beneath the plate) - but it wasn't much. The CZ slide has those sunk holes for the dot screws, so they can accept a tiny bit of protrusion - from what I understand.

So, to sum up, it was probably a bad screw then. I don't know. Now you've worried me about the dot screw protrusion, but from what I understand, that's why the slide has those holes:



, right? To accommodate some of that protrusion? (a little bit of it)

[tdogg]

Ah that makes sense.  I still agree that it is a hardware failure not due to bolt length.

If your slide has recesses then I wouldn't worry about dot screw length.  It looks like that is why the slide has the recess cut into it.

Hopefully you got it sorted and got it sighted in!

Cheers,
Toby

[dabljues]

I still agree that it is a hardware failure not due to bolt length.

Yeah, that's my thinking as well. I took the word of my gunsmith at face value, but he said that it was either a bad screw or a too long screw. But when I was playing with it, I could tell that the 8mm screw is not too long even when screwing it directly into the slide, without the plate.

Thanks for all your input, gotta try out the new setup this weekend, hope everything stays in place!

[Wobbly]

I'd also confirm you are getting the right screw.  The Holosun Comp comes with 6-32 screws, plus the Holosun has a 90Degree countersink apparently?  I don't know what the factory CZ plate thread pitch is but you most likely are correct with the M3. You might need to find the right screw or wait for replacements from the shop.

I don't own and have never used a red dot device (at 73, I proabably should) but as a ME doing machine design, I do know a LOT about screws. So let me point these things out....

• Determining whether the screw is Inch or Metric is paramount to the solution of this problem.
• All Inch-sized screws have a countersink angle of 82°, while Metric screws use 90°.
• An Inch-sized #6 has a thread with a nominal major diameter of 0.138".
• While a M3.5 would also have a major diameter of 0.138"
• It is HIGHLY unlikely that a completely Metric factory in eastern Europe would stop everything to tap some Inch-sized holes.
• It is much more likely that they used a Metric size that is common in Europe, but also happens to be uncommon in the USA.

Me, standing way over here and never having seen the slide or optic in question, and adding my "2 cents" where it's probably not needed would say.... it looks like an American screw was mistakenly used in a similar diameter Metric hole. It's the differences in thread pitch that made the screw jam into the tapped hole.

Bottom Line: Right screw diameter; Wrong thread form.

You wouldn't know all this unless you worked with threaded fasteners in both measurement worlds, which is why the gunsmith didn't spot it.

Hope this helps.

[dabljues]

Huh, thanks for the detailed info on the matter!

I'm still not sure what it was, what went wrong, but I will be more careful when doing this stuff in the future. For now, I tested the gun on the range, 300+ rounds went off, the thing is rock solid. Gotta hope it stays that way