VC Victa,
If it is a late model blade bolt then they have and allen key hole in the blade bolt so that is easy to undo. If you are talking about the old style then that is a different story as you have a diamond type hole in the blade plate.
Now if that hole has been damaged it is going to be difficulty to remove but there is an easy way to do it just put the blade plate in a vice with the nut resting on the vice jaw. You then get a chisel and cut the nut off but if you have an angle grinder then just cut it off.
Next after removing the blade bolt you will have to bur the hole with a round head hammer (metal workers type) and after you have done that the next time you should be able to remove the blade bolt without to many problems.
