I put a hitch on my daughter's SUV this morning. There are a total of 6 fasteners.
4 each M10 - 1.25 x 30 Class 10.9 bolts (Class 10.9 is basically Grade 8) 2 each 7/16 x 14 nuts for a 7/16 x 14 U-bolt (the nuts are zink-colored, might be Grade 8, the U-bolt is silver)As shown in the instructions linked to below, the M10 bolts are used to attach the hitch to the frame via the vehicle's weld nuts and the 7/16 nuts are used with the U-bolt to secure the center of the hitch to the vehicle's tow loop.
Per the instructions, the M10 fasteners should be torqued to 49 ft-lbs and the 7/16 fasteners should be torqued to 70 ft-lbs.
What factors are used to determine those 2 values? Is it the type of fastener? The stresses (shear vs. pull?) The thread sizes? A combination of everything?
The instructions, for your reference:
Thanks for the lesson in torque settings.