That must be the 4 lobe 21T Gold Star sprocket then..Not the 4 lobe 21T M21 sprocket..
..A bit like the maroon Gold Star engine plates I saw at a Jumble...
...Ian
email (option): ian@wright52.plus.com
ian it must be a gold star one because thats what is written on it i mean nobody would use an expensive felt tip pen to write the wrong thing on it would they
email (option): roger.beck@node6.com
Can I point out that I don't think there are any cogs on a motorcycle (or perhaps there are some in a speedo)
Cogs are normally found in windmills Ron
email (option): ronpier@talk21.com
All motorcycles have one 'cog'... Center Of Gravity.. ..The two 'teeth' in the speedo drive are technically cogs as well..and you could argue the point with the tangs on the clutch plates..Ian
email (option): ian@wright52.plus.com
english oxford dictionary COG tooth of a wheel so only one stickey out bit is a cog then 
email (option): roger.beck@node6.com
Your not on your own Roger, I grew up thinking of a cog as the entire wheel & all the teeth, probably from when I was a child hearing the expression caught between the cogs & assuming it meant the the whole thing.
Children nowadays think "lock stock & Barrel" is something to do with guns, I blame the parents.
I do call sprockets, sprockets though 