This is the guide for use on minibuses and coaches - ive gone for 7/16
Quote:
D. Where seat belts, other than looped belts, are anchored to the seat frame or the vehicle floor they must be secured with mounting bolts in accordance with the following:
Minimum Acceptable Size and Grade of Bolts for Seat Belt Anchorage’s
Type of Anchorage
Single Anchorage
M8 High Tensile Steel, M10 Standard Material
Double Anchorage
7/16" Standard Material, M10 High Tensile Steel
Note: Bolt head marks
Standard Material = P, 4.6 or SAE equivalent
High Tensile Steel = S, 8.8 or SAE equivalent
No Markings = Standard Material
If the examiner cannot determine the grade of bolt it must be assumed to be of Standard Grade.
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From memory, nuts are not stamped with a grade anyway. M12 is well above the recommendation, and they really have no way of checking the strength of the nut anyway. As long as the bolt head is stamped, I wouldn't worry!