dh thinks that it's normal for someone as weak as myself, armed with a socket and a box end wrench, to be able to shear off a bolt like that. He must think I'm a superhero. I'll call (didn't get a chance today) and request new ones but in the meantime I may just get ones that are made to be harder. I don't want to have to do all the adjustments again but if I replace them one at a time maybe it will stay put.