one end was at 14mm the other was 17mm here is a pic of the chosen stud with green (lightweight) locktight. the blank or center part is raised, (thicker).

Here it is with the stud tool on installation..

this is the chosen shouldered nut, this part is from a auto belt adjuster/idler/tensioner, not sure what type of car, it was Japanese.

Here it is installed, not pretty as the allen but OH!! how easy it is to install now.. a no brainer, this is especially noice for one (1) small.......... joe..

another pic for you. all comments and suggestions/question are welcome. Peace is what I give you..

as you all can see.... I chipped the coating on the tank tryin to get this f@cken allen back in, now I have gone before you to master this hazardous place.
Just had to decide to open the can of woop arse.