You might find this
According to that, it's 5/8 UNF.
The studs on the back are 1/4 UNC.
Both are available in A2 locknuts on Ebay. Unfortunately nobody on there sells them in A4. I've just had to buy them all myself.
Need spares,consoles,consumables,hire,training or even a new boat?
Please click HERE
and support our Trade Members.
Join up as a Trade member
or Supporter HERE