So, if I tried to get hold of a 7/32 x 32 TPI screw, would I be correct in assuming a Whitworth thread form?
Not really.
7/32 BSW is listed as 24 tpi
And mine - shown above - is that.
(despite a 6mm nut threading onto it quite nicely.)
Your screw with 32 tpi sounds like a 10-32
Is it possible thats its loose enough that only a few threads are catching,
so it feels like it fits ?
( We haven't seen your tank, so anything could have been done to it along the way ! )
P.S. Nice work brightening up my photo there Dave.
My editing prog is on another 'puter - it'd be easier to try for a better pic.