Regina Chain, for use on BSA models: A7, A10, A50, A65 & B33
Size: 5/8" X 3/8" 
Regina Chain: 520.
Links: 98
O.E.M: 110056 / 136SR 530
Note:
Please check the number of links to suit your bike. I have the BSA Chain Guide available in the "Helpful Tips" section.