Hello fella's, I love hearing everyone's methods, I don't have a rattle gun.
To get that off, my approach is to cut the bolt head down, to the next size down socket with a 1mm blade in an angle grinder.
Then I will try to shock the bolt loose with a breaker bar and a big hammer. The way I hold the bar against the blade plate with my left hand is a technique.

If that doesn't work, I chock the blade plate with the right sized piece of wood to stop it moving, and use a pipe extension on the breaker bar. Leverage can be your friend.
Just sharing my methods.
Jaffa, enjoy all the possible fun you can have with that.

Last edited by mark electric; 03/11/14 05:51 AM. Reason: add some details

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