Step 13: Secure frame to rear axle mounts
Bolt the rear axle mounts to the frame using 5/16 inch by 4 1/2 inch bolts, flat washers on top and bottom and lock nuts. Tighten to the point that the top washers are drawn slightly into the wood. Because wood shrinks somewhat over time and there will be some wear, use either lock nuts or double nut. You cannot depend solely on a lock washer and regular nut.