I have just removed 2 bleed valves from a vertical radiator which were leaking. The measurement across the thread was 1/2" so I ordered x2 1/2" replacements from a seller on eBay. They arrived today and measure 3/4" across the thread (as attached picture). The seller is adamant they are 1/2" valves and stated that 1/2" = 21.3mm. Am I missing something here?
Thanks in advance.