Shear bolts are one of the cons for PTO Diggers, they are necessary to save the gearbox but a pain to deal with. I understand our bolts are higher priced but I thought I should mention this first. Our shear bolts are special made for Danuser to give a solid shaft through the connection then threads. The local store bought bolts will have more thread and less solid shaft therefore they will shear easier. I had a customer with the same machine as you and he was going through several store bought bolts and was upset. He called us and I told him the same thing I am explaining now. I described the differences and he did not believe me. So I did what any other "good" company should do, I sent him 3 of our shear bolts. I called back some time later and he stated that he was using the same shear bolt for a week. Now I understand that there are certain ground conditions, diameter augers, etc. that can alter the time for one bolt but I thought you should be aware before you buy from a box store.