Yes the only difference is the two flats and slots on one of them to make it easier to hold the sprocket with a spanner or blade whilst the center nut is done up/undone. Ron
STD725 is the correct dynamo sprocket. It should be used with woodruff key STD572, a special dynamo sprocket retaining nut STD611, Special locking washer STD164 & Locking ring STD708.
STD726 is the sprocket for the magneto armature shaft.
STD727 is the sprocket for the engine camshaft.
All of the above are probably available from Les at Russell motors.
Quite right Peter. Alun's comment about the parts list stating them being interchangeable threw me......I can't see that in the list I'm looking at now and should have looked sooner. Ron