Stripped double bolt - how do I avoid it?

As I was adjusting the seat height on my freestyle uni the other day when I noticed that the bottom bolt of the seat clamp (a nimbus double bolt) was stripped. I decided I could live with just the top bolt, which seemed completely fine at the time. However, in just a few days with not much riding at all, it suffered a similar fate, and I am now left clamp-less.

Could someone explain how to avoid stripping seat post clamps? I don’t feel like I ever overtightened them - it was just enough to keep the seat from wiggling. I have no idea what I could have done to ruin them.

Also, I’ve read elsewhere on the forums that a double-bolt is easier to strip then a single bolt. I may actually buy a single bolt now (Animal Seat Clamp from UDC), but I’d need someone to justify this claim for me.

Long story short, I just don’t want to strip any more seat post clamps, but don’t want to settle for QR.

I think that the nimbus one is made of aluminium (aluminum) which strips a lot more easily than steel, so if you find a alu clamp with a steel insert it’ll be a lot more resistant to stripping.

…and in the unlikelyhood you do strip it, you can possibly replace just the insert instead of the whole clamp (ask if the insert is replacable before buying).

If you are referring to stripping the bolt heads, then the stock Nimbus bolts are crap. They have a very shallow socket, are made of relatively soft metal and therefore strip easily. Make sure you’re using a metric (5mm) allen wrench and not a standard. You can replace the stock bolts with hardened steel bolts from the hardware store. The heads also have a deeper socket for the wrench. I buy them 4 at a time as even the better bolts will eventually strip after repeated tighening.
If you stripped the clamp itself, then you’re overtightening it.

Just wondering how you usually tighten the double clamp.

You should be tightening both at the same time (one turn on the top, then a turn on the bottom, then a turn… you get the idea) just like tightening lugs on a car, if you tighten one too far before you tighten another then you’re creating some sheering problems.

I haven’t had any trouble at all with my Nimbus clamps, though I have noticed they actually deform a little around the bolts! :-o Never affected anything though. . .

it’s really hard to over-tighten those things with a standard length allen key without tearing your hand all to pieces, if you don’t think you’re over-tightening them, then you’re probably not.

I believe this is the key.

I haven’t done a scientific study, but here’s my logic.
I think lossening the bolts in sync might be even more important than tightening.
With two bolts, you are able to tighten each one especially hard. They are helping each other hold more together than either could do on its own. If you then loosen one a lot, not in sync with the other, the one remaining tight bolt is suddenly holding the clamp all by itself… more than it should be able to do on its own. It’s then harder to turn, and stripping the head or threads (in the screw or clamp) is more likely.

The double bolt will strip if the clamp is aluminum and there is not a steel threaded insert, ie Nimbus and KH clamps.

Your best bet is to use a strong single bolt clamp like the Salsa.

I stripped a brand spankin’ new double bolt green Nimbus clamp right before leaving for Utah, the aluminum threads literally pulled out as though it were a sleeve. I replaced it with a Salsa QR and never looked back. UDC sells Salsa clamps.

I have also stripped the Animal clamps and broken bolts. Be sure and lube the threads to minimize friction.

Aluminum threaded clamps are cheap, not meant to be used over and over, esp if you’re using high torque.

FYI, the Salsa QR clamp was rated at nearly twice the holding power of a KH double clamp :slight_smile:

A rounded allen wrench can cause stripping.

This actually makes a ton of sense. I always thought I was tightening them properly (in sync - in fact, it’s hard to tighten just one bolt too much anyway) but I really doubt I was loosening them in sync.

So I suppose everyone would agree that this is worth it? I think that’s exactly what I’ll do. Thanks for all the advice, everyone!

Yeah, Salsa Liplock is strong, I use that clamp on my 26 guni and Oregon, comes in a variety of colors which is nice. The Salsa QR is a little stronger, but only comes in silver.

This doesnt really give you a solution but i always cut my double bolt clamps in half so i have 2 clamps and if one strips i just use the other