You should invest in a set of these Snap-On FDX. Customer was fighting this bolt and rounded the majority of it off. This socket got it without so much a slip or
Snap On - 112TMMSY - KB Tools
Snap+on+Socket%2C+Shallow%2C+5%2F8%22%2C12-Point+F201 for sale online | eBay
14 pc 3/8" Drive 6-Point SAE Flank Drive® Xtra Deep Socket Set (1/8-1") | 214YSFSY | Snap-on Store