Set include bolt extractors to remove bolts sizes: 8mm, 10mm, 13mm, 19mm, 5/16", 11/16", 3/4" in drive size 3/8" The reason I'm posting isn't to praise this product, because many have already done so, but to share my experience of using the tool, in the hope that it helps others faced with the potentially expensive job of removing a bad bolt. During that time I've bought many "wonder tools" that claim to be able to extracted rusty, shredded nuts/bolts, but this is the first one that I have bought that:

IRWIN Bolt-grip 5-Pack Metric and Standard (Sae) Assorted IRWIN Bolt-grip 5-Pack Metric and Standard (Sae) Assorted

When you are faced with a rounded-off, rusted-tight or painted-over bolt, bolt extractors will break it free I opted for a 3/8 extension bar in to a 3/8/ to 1/2 inch convertor, then used a 1/2 inch extendable ratchet to obtain the MINIMUM turning force required to release the bolt. Apply WD40 penetrating fluid to all accessible ends of the bolt , let it sink in, then apply again (repeat every 10 mins for a couple of hours at least). If you can leave it overnight, even better. You are looking for a penetration into the bolt thread, not a soaked drip off the bolt. The time spent doing this is going to be a lot less than if you have to get a mechanic to finish the job. When you are faced with a rounded-off, rusted-tight or painted-over bolt, bolt extractors will break it free. This listing is for the 10504634 base set and the 10504635 expansion set to cover the full range of sizes. IRWIN 10504634 Bolt Grip Fastener Remover Base Set of 5 Set includes plastic case. 5 Piece Bolt-Grip Expansion Set, includes sizes 8mm(5/16"), 10mm, 13mm, 11/16" 19mm(3/4") IRWIN 10504635 Bolt Grip Fastener Remover Expansion Set of 5 Sizes: 5/16in, 10mm, 13mm, 11/16in and 3/4in.

So, here's my thoughts about the prep work required prior to putting pressure on to release the bolt. The gripper relies upon a rotary action, so hammering it into position will likely damage the tool and reduce grip, however a tap to ensure it is seated square may help.