Bench pillar drill. What make?

[Munkul]

heat? impact gun?

 

[merryman]

If it is a stud and the stud is coming out, whatever it is holding will still loosen.

 

[Jonny weld]

heat? impact gun?

Will try to heat, no access with impact gun as you can see

 

[Munkul]

plenty access if you take the handle mechanism off.

 

[Agroshield]

If you want the nut to come off the stud, tighten it back up and wire brush the crud off the exposed threads.

Try tightening it a little until it shifts relative to the stud and then add penetrant.

You could saw a screwdriver slot in the end of the stud to stop it rotating.

 

[nickk]

Could be an Archdale.