Nylon securing nut water tank sender

[blue-max]

I need to  replace the securing nut on the water sender at the top of the tank. Its broken and one half is missing. The diameter of the threaded sender is 37mm which  is non-standard for a plumbing fitting. anyone know where I could get a replacement before I start to improvise? Would also help if I know who makes the sender.

[Nigel]

My sender has the maker's name on it, can't recall it at the moment.

[Yngmar]

Have a split nut on one tank sender as well. Our sender is made by Calira and the bottom of the nut is stamped "29" and "3". SVB has the entire unit, but I just need the nut.

Turns out it's a PG29 thread (37mm across threads), and the keywords to search for are "PG29 mutter". Plenty on eBay Germany (PG = Panzergewinde is a deprecated German thread standard).