Help.
I have a thread on a large drum / tank that I need to copy. As far as I can see its not a 'standard' thread but would love to be proved wrong.
OD is approx 60mm, thread pitch is approx 2mm. The thread does not taper. its not 1.25" its not 1.5"
Anyone have any ideas what it is?

Is it definitely an imperial thread and not a metric 60mm thread with a 2mm pitch

Take a few different fasteners and hold them against the thread for a quick and dirty thread gauge. If they are the same pitch they will sit snugly with no gap.

What's the tank for - might give a clue as to what the fitting is?

2" BSP has a nominal thread size of 2.347"(59.6mm) and 11 threads per inch(2.3mm pitch)

if its in a tank could very well be bsp

good call jimbob

Could be 2" BSP. We originally thought it was a metric equivalent, if such a thing exists?

Its for a steel diesel tank on an artic trailer.

Or 2" NPT which is 11.5 Threads per inch...possible answer if the tank originated in the US or Canada...just a thought

Just got a (kind of) answer from the tank supplier. It comes from France and its a Metric M60, but they are getting back to me about the actual thread pitch, ie is it an M60 Fine.

BSP threads are considered to be a part of the current system of metric threads, despite its origins.