Is there a special tool for holding skin fittings while the inside nut is tightened. My skin fittings are bronze and have two internal lugs for engaging with a suitable tool.
I've just used a suitable 'tool' which engages with the lugs to prevent rotation - I've used a length of steel and a piece of wood or a suitable sized spanner!
I don't want to hijack the thread, but I have a question along similar lines..........my new skin fitting has a single lug on the outside to stop it spinning. I assume that I will need to file a matching groove for it in the existing hole in the hull?
I made a tool from old electrical conduit bent through 90 and a piece of sleeve with a slot. It fits the lugs either from above (seacock removed) or below (two people req'd)
The one with the external lug has been mentioned on here before. I'm less enthusiastic about that as it relies on the hull to counteract the nut torque, and the bead of sealant will not be uniform. Yes, a keyway groove is needed.
Look in the back of your garage, in times past everyone had a sump plug spanner. Looks like a bone with the nobly bits on each end. These being different shaped pieces of metal to fit different sump and gearbox plugs, unless the skin fitting is large one end or other will fit.