A left handed threaded .... thingamy. Looks a bit like a braddle, you screw it into a stuck bolt and as you screw it in so the bolt get loosened.
Might be better to have a look on the bay for another set of carbs

Yeah , thanks Evil, keeping an eye out for another set. Cheers.

Hooray! Finally got the original carbs sorted. Kept bathing them in carb cleaner and blowing air through. Now runs nicely on all 4. At last.

Good news