Ok so I'm building a bumper right now and I'm curious about the winch mount. I have a bracket to hold the fairlead but the bolts are like 7/16 or 3/8. Seems under sized to me. It the winch all shear load ?

Is it bottom mounted? If so then a fine thread will have more sectional area to the bolt hence a stronger connection for shear. Plus you know then you might want to go grade 8. I used to use a socket head if i wanted the high strength because they have a higher tensile strength than a conventional bolt unless you go grade 8.

The fairleads don't generally see too much force. But go grade 8 if you're worried.