I contacted Realcyclist.com and they are taking the bars back and gave me a free shipping label.

it was a good lesson learned. Now I will be ordering some alum bars.

Aluminum bars can fail too. The only bar failure I've seen in person was an aluminum bar (broke during a crit). One of my Cutter bars has been wrecked, uninstalled and reinstalled multiple times with out a torque wrench, and is completely fine.

They can, but I've seen many more broken carbon bars (in bike race crashes) than I have aluminum ones.

In crashes perhaps - but all bets are out the window in a crash as forces outside of normal spec are applied to the bars. I'm talking about breaking during normal installation and use.

Really? The two carbon bars I've had have booth been 5 Nm, or 5.5 Nm for the one I'm riding now. I had assumed all carbon bars took ~5 Nm; it seemed like that's why they made that torque key?

Your stem has a max torque of 5 Nm before you start to strip the threads on the [baby bike] bolts, but it doesn't require 5 Nm.

Anyway, I suspect these were defective. Or didn't fit the stem well. Or something like that.

+1 - I think it was a single defective bar or stem.

...my torque key is a Bontrager 4Nm, and the bars I was installing were Bontrager xXx... and it still cracked the bars... as for improper tightning... I just installed it like I would lugnuts on a car... crisscross at small 1/4 turn intervals... as for the stem being out of shape, the new bars went on like butter @4Nm with no prob... I would assume there are as many torque keys as there are torque ratings...

Well there are torque wrenches where you set the amount of torque you want to apply. I use one of these to do my 4.5 Nm seat post. I think the idea of a torque key is that it's cheaper because it only does one thing; it's useful for your bars, but not for much else. So I had assumed that 5 Nm was pretty close to universal.

I crushed a carbon seatpost using one of those stupid ritchey torque keys. Never got to the point of the key clicking, but the post had a definite crack in it. The fault was probably relying one of those those POS keys. I threw mine away after the post got crushed. Haven't crushed carbon since.

I have one of the POS keys... i hope I don't crush my seatpost, or frame.

Did the instructions for the bars say to lubricate the threads? If not, then it was reasonable to torque the bars without lubricant. Do all of you lubricate the threads on all your bolts that you use a torque wrench on? I doubt it. We've all seen guys at the LBS who do this for a living adjust bars and seats for customers without a torque wrench.
I think some of you guys are looking for ways to make this the fault of the installer instead of a fairly fragile part. As I've said before even a top notch manufacterer will make a bum part once in a while and it sounds like the OP got one. It doesn't matter that the MAX torque spec was 5 and he could have gotten away with 3 or 4. If the bar cracked before 5, then the bar failed.

What kind of company is Cutter? The only website I could find was https://www.cutterbike.com/ but they don't list any handlebars and look mickey mouse.

1/4 turn interval is way too much for tightening small bolts like that. On a 3mm bolt, you are moving .5mm/turn, so 1/4 turn is .125mm. Once everything is tight, 1/4 turn means you are deflecting your carbon bar clamp .125mm; you don't need many .125mm movements to crack something.

This is why wrenching takes some practice. You always lubricate bolts. If you don't, you have, literally, no idea how tight your bolt is. And again, the "torque spec" written on the stem has nothing at all to do with the bars. The max torque spec is for the screw threads so you don't strip them, nothing more.

I believe that it is Realcyclist.com's house brand.

So you are saying that 1/8th inch wall thickness carbon tubing is not going to be stronger than 1/16th inch thickness tubing? NO offense, but that doesn't sound right.

Not necessarily. It depends on the quality of the layup and how the curing process was carried out. Is 1/8" stronger than 1/16"? Maybe yes, maybe no. Point is there are more variables for composites than there are for metals.

This is really splitting hairs. OK, lets pretend that the quality of the layup was similar and the curing process was appropriate for carbon of that thickness. All other things being equal, the thicker wall tubing is going to be stronger.

This is a pdf from specialized:
https://cdn.specialized.com/OA_MEDIA/...ion_OL_1pg.pdf

Doesn't mention lubricating the installion bolts of a carbon road stem. Not saying that it is wrong to do it. I'm saying that it doesn't appear to be mandatory to the installation of their stems. Perhaps the OP can tell us if the Cutter's instructions recommended lubricating the threads.

The end of that pdf says that visual inspection of carbon fiber is difficult that and if there is reason to think the bar is damaged (wrecked bike) that it should be inspected by Specialized even if there is no visual evidence of damage. That bar was toast the second they heard crack. Even if they had inspected it and found no visual damage, they should not have put it on the bike. It should have gone in the mail back to the seller or into the trash as a lesson learned. You'd be nuts to trust a bar that you heard a distinct crack during installation even if it looked ok to you.

I prefer to buy parts for a mission critical application from someone I can sue if there's a problem. Realcyclist is an internet retailer and doesn't seem like they'd have very deep pockets relative to Easton. I suspect their R&D for this part consists of someone picking a part from a Taiwanese catalog. Not very comforting.

It is pretty much always wrong to not lubricate bolt threads. Sure, you can get away with it. But again, if you don't lubricate threads, you really don't know how much bolt tension is on the bolt. There is no way to tell because friction on unlubricated threads can vary by huge amounts.

Well yea, sure, if everything is the same except the one thing that is bigger, then the bigger thing is definitely bigger. Not a very useful analysis though.

Good info and advice.

BTW, you list your location as south of Salem and north of Eugene. Do live in Albany but don't want to admit?

do whatever you like - no skin off of my nose. My post was just informational about the origin of the Cutter brand. I do use this product though and have had a positive experience with it. That's also just informational.

FWIW Realcyclist.com is owned by a fairly large company. They own several fairly large sites including Competitive Cyclist.com.

I agree with you. When torqueing a bolt, the proper way to do it is to lubricate the threads. I also agree that if you choose not to lubricate, "sure you can get away with it." That just reinforces that this is a fragile product. If the difference between proper installation and catastrophic failure of the product is a few drops of lubricant on the threads, it's a fragile product (or a defective part more likely).

I'm not saying bigger, I'm saying the thicker wall tubing is stronger.