Brass 1/2 inch BS1212 part 2 float valve / ball-cock complete with float.
High pressure, suitable for mains pressure water.
Use in heating feed and expansion tanks, cold water storage tanks and toilet cisterns etc.
A bit quieter than the part 1 version and better suited in applications that need to prevent backflow (toilet cistern and F&E tank for example).
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.