1/2x28 means 1/2" x 28 tpi or threads per inch.
Anything measured at 1/2x28 will fit on any barrel threaded at 1/2x28.
The only thing the specification does is not specify the depth of the threaded area. So in theory you could have a muzzle device that's not deep enough to cover all the exposed threads on the end of the barrel etc. but that's uncommon.