rusted bolts
If you have the Bolt That Will Not Undo, (ie in a cylinder head, pipe flange or similar) take the pressure off it by tightening the other bolts around it. Don't take them out first, it will make it worse. Also, if it really won't move, smack it down on the head hard with a hammer to drive its threads out of engagement with whatever it's in. If this doeesnt do it, nothing will.

Also - Use a ring spanner, or a true-hexagon socket. Open ended spanners and - worse - adjustables, will slip and remove two corners from a bolt head. Avoid.
(Jack Rarebit ...We like chillies, Sun 3 Dec 2006, 23:49, Reply)