This tail screws into a radiator using suitable jointing and connects to a standard radiator valve.
The male thread is 1/2 inch BSP and the fitting has a compression nut and olive (included) to suit a valve with a 15mm compression fitting type outlet.
Will not suit a union type rad valve with a bigger 3/4 inch BSP outlet.
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.