Replacement Valve Question

[PghNinja]

I have to replace some radiator valves in my house - I was wondering if there was a part available to just purchase the 3/4" cap on top of the radiator pipe and the turn valve, or would I need the entire assembly? I have a picture attached below.

 

[user 4883]

While conceptually the same, the guts differ from maker to maker. Replace the entire assembly.

 

[billshack]

It looks to me like a dahl valve but the old design , they have changed it to a more modem look. but you could try buy one and seeing if it fits.
https://www.dahlvalve.com/products/radiator-valves/regular-pattern.php