Seatbelt bolt safety

I would just snug it down tight and call it good. If you're really paranoid about it you can always consult a torque chart for the size and grade of the bolt.

 

With stuff like that where I don't plan on removing it frequently, if ever, is to coat the threads with some Loc-Tite red (or similar) and then tighten the bolt down until it stops then give it another 1/4 to 1/2 turn.

http://www.loctiteproducts.com/p/10/15/t_lkr_red/overview/Loctite-Threadlocker-Red-271.htm

 

I had a chance to speak to a mechanic this afternoon. He told me there are no official specs on this tiedown bolt but he always torques to 35 ft pnds. Edited to add he advises against using anything but a lock washer.