On loose carrier key screws

**mtdawg169** · 04-04-17, 10:10

Originally Posted by Wallace's

Aren't those for safety wire applications? I have seen fasteners like that on race cars and aviation type applications.

Must be a really old spec. I've only seen those safety wire screws on very, very old M16s. And it was a grip screw, not a gas key screw. I always assumed it was used because that is what was handy back in the day when Stoner was with Fairchild / Armalite.

**mtdawg169** · 04-04-17, 10:12

Originally Posted by Ned Christiansen

Data, yes, keep in mind that everything depends upon everything else.

I've done just few tests on the "mil spec" screws for a few reasons, one, I figured they were good and they are, but they are seldom seen except on the brands that do staking right. The other reason is, what I'm telling my screw customers:

"Buying American-made socket head cap screws is a reasonable assurance that the required standards are being adhered to. With some off-shore brands this has proved to be hit-or-miss and in some cases, actual counterfeit fasteners with falsified traceability and quality documentation have been discovered in customs, or when they failed in their application. Buying screws that have the appearance / outward features of the mil-spec screw may carry no assurance of standards compliance unless the actual source of the screws is known and trusted."

What I'm saying is, if we don't get our mil-spec screws from a known source, it's not really possible to say they are for sure the real thing. When you get commercial screws with a brand name on them, you know who made them and they have a vested interest in making them right. Otherwise all we would generally have to go on would be "haz 1/8" socket" but that's about it. I'm not saying I know there are fakes, just saying that, well, I don't know, and I don't think anyone does who is not getting them from a source that can provide documentation.

I will say that in 6-plus months of talking to not just screw companies but also sales reps who rep for cold-heading manufacturers, when I got to the description of what I wanted, a common reply was, "Oh we can met that done for you at one of our off-shore houses, you will be very pleased with the pricing!" That's when I knew I had to deal direct with an existing screw mfgr. of long standing good repute. It goes without saying that they would be a US company!

So Mil-specish screws, the few tests I've done on them, with good stakes, they come in at avg. 110 in pounds. Again the install spec is 50-58 inch pounds and breaking torque spec is 50-100 inch-pounds. So that's pretty good.

Everything depends on everything else part deux: Carrier key tolerances on the rebated part where the staking goes, are wide open. The width range is .022 and the height range is .012 without even considering the tolerance on the carrier diameter and the height of the surface the key seals on. So if you get a narrow, low one, the stake will be less of a stake, pure and simple. Hardness plays a role too-- I've seen some that were file hard for some reason. I suppose there are those that are too soft, but the three or four I've Rockwell tested happened to all be within the 26-32 range.

The ubiquitous YFS screws have not fared well in my testing, as expected. They averaged 76-- in spec, but these are by far the ones I most see loose. That is also partly because there is some correlation between the mfgrs that use YFS and staking thoroughness too. But the YFS has bogus knurling and a rounded head. Maybe an OK screw but not as a carrier key screw. I thought it was interesting that a completely un-knurled 8-32X 1/4 cap screw, with splines, soundly beat the YFS screws at 90 and 96 inch-pounds breaking torque!

Data on the OCKS was a very consistent 132 inch pounds breaking torque, that is with the screws installed at the very bottom of the 50-58 inch-pound installation torque range. I will be conducting about 160 more tests in the coming weeks.

The bottom line though is the breaking torque spec. As long as my carrier keys are not coming loose, I don't care if they key is wide, narrow, low, high, or a few points too hard or soft. Splining the screw heads reduces the criticality of the other factors.

Thanks Ned. I obviously assumed that the removal value would be higher with the OCKS. I was just curious as to how much higher. Color me impressed!

**Ned Christiansen** · 04-04-17, 11:07

In the next round of testing I will try to test some installed at the middle and top of the installation torque range. Meantime I hope to get a chance to break-torque test a few with YFS screws and 'typical' factory staking. I won't be surprised to see those come in well below 50 inch pounds.... I know I've run into many over the years that I don't think would register at all on a torque wrench.

**bamashooter** · 04-08-17, 14:55

I'm just a shooter who happens to have an insatiable appetite for high quality fasteners. And a great appreciation for those who "think outside the box" (hate the term nowadays). Believe you exceeded both. Perhaps I missed it. When will these be available? Congratulations.

**Ned Christiansen** · 04-10-17, 10:35

They have been and are available, just email me.

**bamashooter** · 04-10-17, 20:15

Originally Posted by Ned Christiansen

They have been and are available, just email me.

Ok. Thank you.

**Ned Christiansen** · 04-23-17, 11:20

I started wondering what breaking torque would be with no staking so I did a little test the other day. I remember doing this in my early motorcycle wrenching days with sparkplugs but I was less scientific about it and of course the results are long forgotten.

So: take 8-32X1/4 screws and torque them to X installation torque, then check the breaking torque, No staking, no locking compound. Averages of five tests each:

Inst. tq.... Breaking tq
50.......... 32
55.......... 35
60.......... 36
75.......... 44
80.......... 45

In another test earlier this year, the mil-spec screws I had, source unknown, started stretching and breaking at an average of 62 inch pounds, with a low of 60. Just two inch pounds over the max installation torque.

All commercial brands tested started stretching and popping heads off in the low 80's. This was consistent in all brands.

Conclusion, without staking, you can't get them tight enough to meet the breaking torque spec. They will break first. I don't get why some outfits are still not seeing this.

Anyone wanting to try the OCKS, I'll send you a sample pair, the first 50 takers. But you have to make it easy on me. Email me your name and address in a clear and easy to copy and paste format, I'll get a list going and send them in bunches, so don't expect them to ship right away.