Replacement tap size?

Hi Folks,

I have a largish galvanised tank hidden away in the back corner of the garden. It collects water draining off my shed, but because I have other rectangular tanks with more convenient access this one gets used very rarely. It was in fact the first tank I installed, scrounged many years ago when I was broke & couldn't afford a new one. It's still in quite good condition. I did buy a 'ground ring' to use as a base so the tap is raised off the ground at bucket height.

My problem is that it uses a tap with the rather old fashioned 'conical' quarter turn valve & has no threaded hose fitting. This valve often seizes up requiring a decent blow underneath to dislodge & loosen it up. My wife constantly complains that she can't turn it (it's the closest water source to her potting table) so I want to replace it! However I'm having difficulties figuring out what size replacement fitting to buy.

I want to replace it with a similar quarter-turn tap with a ball valve (nylon or brass), a long lever handle & a screw-on hose fitting. The current tap measures 32mm across at the hexagonal base of the casting with (I presume) an externally threaded inlet screwed into the internally threaded fitting soldered to the tank (about 36mm diameter). I've attached some pics which show what I'm talking about.

Can someone with experience with this sort of tap please advise me what size replacement I need to look for? I'm guessing it's going to be either 1" or 1.25" in the old measurement...

thanks,
Sam.