Morris Minor Owners Club

I have noticed that my rear seat rest on a two door saloon is held in by two bolts stcking out of the back of the actual seat, they go through two holes in the metal and are then held in place by two wing nuts. BUT when I tried to take them off they both snapped! My questions is what size 'headless' bolt goes into the captive nuts in the rear seat? And what size wing nuts? Are they 7/16?

I'm presuming that the headless bolt goes in first then you put the seat in and align the bolts with the holes then you put the wingnuts on?

Thanks! x

I seem to remember that either in the club magazine or Morris Minor Magazine someone is advertising a stainless version of these with integral washer