Solid state rectifier to fit 12 or 6 volt,positive and negative earth alternator equipped bikes with a single phase two wire alternator.This part is known to work for many years and is the normal type supplied for old British bikes.Beware of other part numbered rectifiers and if in doubt,ask the seller if another part number will prove reliable over long periods of use.Even ask to see one fitted on his bike.
I ride classic bikes as a hobby and associate with hundreds of old codgers riding around with these rectifiers as replacement units.
Member of E.C.M.C club and always on the E.B.M.C club meetings as well as V.M.C.C meets.
Buy a part you can be sure of or maybe buy one a little cheaper and hope you have a fire extinguisher nearby when out on the road.
Buy from a classic biker  who actually knows what the part does.Pictures show my T120r in 1978 with my young son now 40. Plus my other bikes in 2015.
First class post on day of purchase for fast delivery.