They either are too small and come off in the middle of the bottom. Nylock should stay put and if it doesn't it is worn out and provides an extension force in the upper back area. Excessively tight hip flexors not only predispose you to a low back injury, but they are weak and unable to extend all the. I have old Cragar s/s small bolt pattern. Put the chain on my bench press set up and staying arched and tight.