I had my second IRO nut crack on me today. I torqued the nuts/washer down and the damn thing snapped. I am sure I used a bit too much torque but the soft metal seems like a safety concern. Is there anything wrong with using regular washers/nuts on the axle. No shop within a 50 mile radius had the proper track lock nuts so I just went to the hardware store. I bought expensive washers that aren't changing shape. So far so good. The damn IRO cone nuts seem to be flimsy. I probably shouldn't have torqued them down as hard as I did but oh man what a tragedy it was to hear the SOB snap. I'll have to drive 15-20 miles to get a new one. I wish I could forgive my local bike store but they are SOBS! When I win the lottery I will open a new shop and employee only alcoholic fixed gear riders who do nothing more than build wheels, install cogs, clean chains and deal with primitive 1 inch headsets.
happened to me twice too. the first time i had tony send me one, which he did no prob. the second time i just found a serated one at the lbs that worked.
they're brittle for sure, but it's key to have em snugged down.
i'm sure for a couple bucks tony will send you a handful if you call him and ask.
they crack because they are hard not because they are soft. That hardness will keep them from slipping better then the softer ones you can pick up at an lbs. So you can either not crank on them so hard, replace them frequently, or just go for the cheapo softer ones. If if it's not slipping just be gentle or get the soft ones. If it is live with replacing them or get chain tensioners.
+1 on tensioners. I cracked two Surly locknuts and riding on that was starting to **** up my dropouts, so I got scared and got a tuggnut. Now I can get away with much, much less torque, and as a result i have had no locknut crackage problems since.