I have a Stainless Steel Pear screw link. The one New Tribe sells for $36.00 (ouch.) It is about 2 years old. About a year ago it started to get a little tight to turn, but not too bad. After a climb last week it seized up and will not turn even with a wrench. I've always kept it closed to protect the threads. There is no observable thread damage. I have never loaded it in the open position.

EXCEPT

When we were picking up our gear last week, I forgetfully lifted my harness up by the link while it was open. I don't know how much my harness weighs - maybe 15 pounds or so. I've never weighed it. When I got home, the link was uncloseable. Should I believe that lifting 15 pounds with it opened, destroyed it? Are they THAT delicate? These things are rated for over 12000 pounds.

To order a new one with shipping is right at $50 bucks!!

I've had it happen to 2 non-stainless pears (I don't own any stainless versions). My current pear has been stable for 3 years, I very rarely open it. I tried putting one in a vice and applying a hammer tweak to see if i can realign the threads, no go. Might be worth asking NT for comment on the issue.
-AJ

I don't think you could have possibly tweaked the link by lifting your saddle by it when open. My guess is the threads are galled and have seized. It happens when the friction between two surfaces of like metals causes tiny points of cold-welding. Once material starts adhering to the other surface and tears away, the process increases exponentially until things can't move anymore. All non-lubricated, non-coated like metallic surfaces can do this, but stainless steel is among the very worst.

If that is the case, and you need to remove it, you may as well hacksaw it off, because even if you manage (using heat, penetrants, etc.) to get the threads moving, they will never work properly again. If it seized in the open position, consider yourself lucky! Based on my experience with stainless steel threads at work, I am really surprised that this problem doesn't happen more often with climbing delta and pear links, because I don't think most people pay much attention to lubing them. Including me!

It seized in the open position.

I'll definitely talk to New Tribe about the problem Tuesday. I've got some old links that are over 25 years old and are as smooth as silk. This one is on the front of my saddle and I have to open it every time I put the saddle on.

Oiling it would not be a problem. I just didn't know it was needed.

Hummm? Swamp Fox and I have about two dozen NT saddles for kids and youths and we host somewhere around 60-70 events a year. And every year we've replaced four or five deltas; we always assumed that some fat kid swung and jumped up and down too much while the gate wasn't completely screwed shut. Swampy put a few of them on his 20-ton shop press and tried to straighten them, with only minor success.

After reading Dietley's comments, I'm beginning to think that cold welding could be the real culprit and lubrication could be the solution.

My question: Which lubricant would work best -- graphite, oil, synthetic, etc.?

Amen to that!

Lubing a screw link can be a double edged sword. While it does protect against galling, it also reduces friction significantly. If you don't get the screw gate closed with sufficient force, it can unscrew much easier than a non-lube one.

I used some high-tech gun oil on my Zircon delta and it smoothed out the openning and closing dramatically. It's also very easy, almost too easy to open and unscrew. Remember, for the case of a screw link, in normal load bearing situations such as climbing, it never tightens up, but it can loosen with all the cycling. Once it looses a bit.....

Experts like New Tribe or On Rope 1 might have a better answer, but I'd think that a dry lube like graphite, or a synthetic product with silicone, or similar, would help, and would be less likely than a petroleum-based product to end up all over the saddle, rope, and hands. A lube like the purpose-made anti-seize ones would be best for the threads, but would likely result in an awful mess. Some sort of compromise lube would be the best!

Remember, too, that wet or sticky lube will cause dirt to be collected in and around the threads, and that isn't great, either.

Oh, hi, Ron! Guess you posted while I was writing. I didn't mean that experts like New Tribe or On Rope 1 might have a better answer than yours!

LOL - "timing is everything".

I spoke to Barbara at New Tribe today. She really did not have a good answer. (Meaning she doesn't know why it happens) According to her, the only ones that come back with this problem are the pear shaped links. She said that she thought that because of their shape, they were more likely to bend just enough to get out of line.

I have trouble believing that my 200 lbs is bending a 12000 pound rated piece of steel. And if that is the case, oil or graphite won't help.

She says she sends them back to the manufacturer for a replacement and then she will replace mine. I think I'll keep my next one lubed a bit, just in case the cold-welding theory is the correct one.

According to her, she has never had a problem with the delta's - just the pears. But several here have said they they HAVE had the same problem with their deltas.

So while she couldn't answer the question as to why it happens, she was very helpful and willing to replace the link. (New Tribe are good people)

So I guess the mystery remains??

I would assume that if the nut could turn freely, but wouldn't/couldn't start on the threads when closing the link, that bending was the issue. However, I was under the impression that your link was seized in the open position, which would take more than a slight bend to cause.

I should point out that a bent frame could be the cause of the problem, and the cold-welding seizure be the result. Anything that increases friction within the thread interface can lead to galling: clean, bare metal surfaces; foreign material getting jammed in; misalignment; etc.

If anybody has a seized link they want to diagnose, send it to me and I'll cut it apart so the threads can be examined. Just don't expect it to remain useful after the procedure!

Mine will barely start on the threads before seizing up. And I do mean barely.

Too bad I can't cut it into. Then, if bending was the problem, it should screw together easily.

For sure there is no way you deformed this link by lifting your harness with it open. You could climb all day with that thing open without deforming the link.

I also don't think the cold welding thing could happen. My understanding of metal is minimal. But a link never pushed to more that 1/30th of it potential. Occasionally opened and closed- no way. Can't happen.

Could it have just been stripped?

Um, maybe consider punting that darn heavy hunk of metal and just loop a runner thru all three? I hate screw links regardless of size, shape or alloy.

I've had to 'tweak' my delta occasionally and, remembering this thread, decided to make a few simple measurements that might be of some interest:



Screw-links can become too 'tight' to use. All pears, deltas, and oval screw-links are susceptible (in that order) to linear mis-alignment, that is, too much or too little open gap in the link.

Measurements were made on ONE dry (un-lubed) stainless-steel delta to determine the relative effect of linear mis-alignment on the function of a screw-link. Only linear mis-alignment was measured.

It was found, on the one sample, that as little as +/-.005" had a significant effect on the 'tightness' of the nut. As little as +/-.010" can render a screw-link too difficult to use and +/-.015" can 'lock-up' a screw-link completely.

It was also found that increasing the gap is very much easier than reducing the gap. It was surmised that this was the result of some residual stresses from the process of cold-forming the link. This may explain why some screw-links become difficult to use if loaded (even lightly) when open.

It is generally considered good practice to NOT USE OIL on a screw-link. Dry lube is considered acceptable. Keeping the threads very clean is usually sufficient.

All screw-links are susceptible to galling (often over-stated as 'cold-welding'). However, stainless-steel screw-links are much more susceptible to galling than the alloy steel (zinc plated) screw-links.