Petter AC1Wm stop

[AlmostRetired]

Hi all. I recently acquired a sailboat with a petter mini 6 and was wondering if anyone knew what size nuts are required to put the stop cable plates back in place. The only way I can stop the engine, is to reach inside and push the injector cut-off up instead of pulling the stop button cabled to the two plates hanging there. Previous owner says he dropped the nuts and just left it off. I would like to be able to stop it from the cockpit properly. I have tried various sizes, but the mounting bolts push back a lot and it's hard to access, so it's a tiring job trying bolt after bolt.