There are several 'wonder sockets' on the market for removing seized nuts and bolts and after many failures we came across these American made items. The design is quite simple, the forks inside the socket are driven inwards by cams as you apply force to the socket. That means the harder you try and turn them, the tighter they grip! Whats more, they drive on the faces of the fastener, not the corners, so even quite rounded off nuts can be gripped. If these won't get them off its time to get out the grinder (or if you're not in a hurry, immerse in some IReOx for a few days and unbolt normally).
You can use them on good nuts and bolts without damage too, which is a bonus. They are also useful if you are reaching into a tight area as they grip the fastener so it won't fall out of the tool.
High quality chrome vanadium (really nicely made). 3/8" Drive.
Size in this pack: 3/8", 7/16" (also fits 11mm), 1/2", 9/16", 5/8" (also fits 16mm), 11/16", 3/4" (also fits 19mm) + 10mm, 12mm, 13mm, 14mm, 15mm, 17mm, 18mm.