You are ment to replace but lots of people reuse them, they do stretch so specially under more power , also were the cam cap bolts slide over little guides and that's were the thread is for the cam cap bolts there not aluminium, magnets stick too it were it won't to the head?? Also I have 2 xr6 turbo motors ones a ba ones a fg there both torn down both the same $106 bucks for all new ones from Ford just found out so I'll be ordering them and play it safe. If I could figure out how to upload picture on here I would, also if rebuilding a head or motor why reuse bolts and parts wouldn't you rather use new ones specially under lots off load just like you do with head bolts and , con rod bolts and main cap bolts if rebuilding a motor wouldn't you use new ones?