During a winch clinic that I was teaching we had a winch shear off a 3/8 winch bolt and bent two other 3/8 winch bolts. Make sure you or the manufacture uses the correct grade of bolt for your winch size, winch plate and front and rear bumpers. After checking and replacing my 18 bolts with all grade 8 bolts; I found I had 6 Stainless Steel bolts, 4 grade 8, and 8 grade 5 bolts. The interesting thing is the bolts that held the winch to the winch plate was SS and those came from the manufacture. I guess the best advice is "check your nuts and bolts"!
ROCKCRAWLER.com - Grade 5 vs. Grade 8 Fasteners
eBay Guides - Stainless Bolts--Usually very weak