A Talon special engine sprocket for the BSA C15 and B40, with just 18 teeth to reduce the gearing for trials and off road use. To use this you will need to reduce the standard primary chain length from the standard 70 links to 68 links.
In addition you will need to adjust the depth of the oil seal housing by about 2mm. If you bolt this straight on the primary chain will foul the crankcase on the oil seal housing.
A thinner oil seal is also required for the shallower housing, which you can choose to add via the dropdown box.