Bought some new stainless M10 nuts and bolts to fix brackets to the rear cross member. Bolted them down no bother. Finger tight first then spanner and socket/wrench to finish. Decided to put a larger diameter washer on them, so unbolted and swapped washers except for one! The nut initially started to wind off no bother, but then quickly developed resistance close to the end of the bolt. Became impossible to move loosening or tightening. Had a few spare nuts, so contemplated using the angle grinder to cut the nut off, but everything is galvanised and didn't want to catch any of it. Soaked it in penetrating fluid, put a socket on each end with longer bars and tried to force it off, but the bolt sheared.
I was loosening it hellish quickly initially before it seized, but no idea what happened. It wasn't cross threaded.
Any ideas anyone?
I was loosening it hellish quickly initially before it seized, but no idea what happened. It wasn't cross threaded.

Any ideas anyone?