Brass 3/4 inch BSP BS1212 part 1 float valve / ball-cock.
This bigger than normal valve is more usually found in an industrial environment.
Threaded ball mounting end has 5/16 inch thread - use a 6 inch float.
BSP (British Standard Pipe Thread) sizes don’t match up with what you would measure using a ruler. Have a look at the BSPT link at the bottom of this page for more information about how plumbing threads are measured.