no3 cylinder bung
 

can someone tell me what thread size is used on the no3 cyl bung please.

fairly certain it's M18
Trev

That's what sprung to mind for me, too.

If you want an adpator, various places do them.

Deffo M18

i got an adapter with the temp sender but it doesnt seem like a tight fit.

Wrap it in layers of PTFE tape. Make sure the tape is wound so it TIGHTENS as you screw the adaptor into place, rather than UNwinds.;)

You are maybe used to coned adaptors which tighten as you thread them in? This one is a parallel thread.

im used to no adapters at all, lol. first time actually taking engine related parts off to modify. suspension, brakes etc, easy. removing alternator to add remote t piece for pressure, easy. removing intercooler to get at that bung, a git! but then the adapter kinda 'plopped in' doesnt really bite at all. thats what worries me, will need a fair bit 'o' ptfe. does that sound rite, and putting ic back on was a nightmare, bust the elbow for recirc valve in process. lol. cars!

No, doesn't sound right at all :(

Mine, you could thread it in easily. Once I got tape on it, it was a socket to turn it.
I'd contact the seller and find out what it's for, maybe get them to change it?

Plenty of places do the right one, they need to know what the adpator is for and either the thread, or the make of the sender.