This is a proprietary reproduction open 'megga' exhaust trumpet with a small reversed lip at the end. It is 1.750" exhaust bore, so will fit Norton SOHC bikes, and as it has no baffles fitted should make a very fruity noise!
It is not actually based on the original Norton Manx megga (see my Big Plunger Manx on our RacingVincent site to see what an original looks like), but is well made, has good quality chrome and has a mounting bracket at the rear. It also comes supplied with reducing sleeves in case you want to fit it to a smaller bore pipe - 1-3/4" reducing to 1-1/2" and 1-5/8". I also sell a similar version with inner baffle fitted. Last photo shows megga loosely fitted to my 37 Inter build . . . not the best photograph as the exhaust is fouling the build platform, but gives an impression of scale