[Tim B.]

Leathernek. More options from the peanut gallery. I'm with the Bolts should be fine guys on this one. But with the don't countersink the frame guy's as well. As for head height above the frame a 1/4 inch rivet requires a shop swaged head height of .080 to .170 in and diameter of .330/.430 in for max strength. I suspect this is in line with the original head height. If you don't want to countersink the frame or grind a bolt head down A 1/4-20 ASTM 307 square head bolt has a head height of 11/64 or.1718 inch. Low-Strength Steel—ASTM A307 Grade A bolts have a plain finish, minimum Rockwell hardness of B69, and minimum tensile strength of 60,000 psi. Make sure the frame and crosmember flange mate without a gap. Put a self locking nut on the bolt (without locktite) or a nut & lockwasher and torque the bolt. The danger with overtightening the bolt is you have increased the bolt preload and reduced the yield strength. The additional shock from a pothole could cause the bolt to yield. Over torquing a bolt with lock washer & nut may feel good as well but it negates the effectiveness of the lockwasher. Use the locktight if it makes you feel good but it's easier to take things apart without it. The advantage with the square bolt & nut is you can probably squeak a wrench in and check the bolts if you decide to without tearing things apart. If you end up wanting to rivet in the future the frame isn't countersunk. A bag of 15 bolts is about $6 at McMaster Carr. Tim