Brass 1 inch BSP mains pressure BS1212 float valve / ball-cock.
This is an industrial sized valve, you're very unlikely to have this in your house (unless you live in Buckingham palace).
Threaded ball mounting end has 7/16 inch British Standard Whitworth (BSW) thread - use an 8 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.