DV:
From the Simpson web site:
" Mounting brackets should be installed at an angle that is compatible with the direction of pull on the webbing under full load. Preferred mount is in a double shear with allowance for the bolt-in bracket to pivot and align toward the direction of the load as shown in Figure 1."
" Minimum specification for bolts and washers to attach the seat belts, harnesses and anti-submarine belt hardware are Grade 8. "
http://simpsonraceproducts.com/safet...ting-brackets/
GrassRoots Motorsports: Mentions follow the vendor specs, but no specifics on the bolts
http://grassrootsmotorsports.com/articles/black-belts/