They're 3/8-16 Grade 5 bolts- - - - -30-35 ft/lbs. should be about right. Any standard hardware torque chart should get you in the ball park.
ASTM A449 / SAE Grade 5*
Bolt Size TPI Proof Load (lbs) Tightening Torque (ft lbs)
Galv+Waxed Galv Plain
1â„4 20 2,700 2,025 4 11 8
5â„16 18 4,450 3,338 9 22 17
3â„8 16 6,600 4,950 15 39 31
7â„16 14 9,050 6,788 25 62 49
1â„2 13 12,050 9,038 38 94 75
9â„16 12 15,450 11,588 54 136 109
5â„8 11 19,200 14,400 75 188 150
3â„4 10 28,400 21,300 133 333 266
Jerry