Reflex shock
 

Want to make shock stiffer. Don't have the correct spanner, what's the best alternative and will larger number be stiff ? Was thinking channel locks but I imagine these ugly gouges?
Some advice?

The fix
 

Got motivated today. Used these 6mm bolts and jam nuts. Insert them 180 degrees apart in the holes provided. Carefully grip them with channel locks and turn, one detention at a time. Higher number is stiffer.