Brass 1 inch BSP mains pressure BS1212/1 part 1 float valve (also known as a ballcock, inlet valve, fill valve or ball valve).
This is an industrial sized ballcock valve, you are very unlikely to have this in your house (unless you live in a mansion).
Threaded ball mounting end has 7/16 inch British Standard Whitworth (BSW) thread - use an 8 inch float.
** BSP thread sizes are measured a special way - have a look at our information page for more details **