I'm trying to replace my cat converter but I can't get the damn spring bolts off. They just spin, but make no progress coming out. Anybody have a good technique to deal with this?

Do you have a wrench holding the nut on the other end ?

Use a cut off disk to cut the bolts.

Replace all hardware with stainless steel.

I had to cut it off with a grinder. Anyways now I have new problems to deal with...

i replace literally hundreds of spring bolts a year in my shop. they snap all the time. oreillys and most part shops have spring bolt replacement kits for <$25.