Single row ball bearing used on all Single Cylinder models (pre-full width hubs) on the plain hub side front hub and also on the brake side for pre-featherbed conical (SOHC Manx) front brakes. They are also used on all rigid\plunger\non-conical rear hubs on the non brake drum side.
As always, this bearing is a high quality named brand bearing (i.e. not a chinese bearing!)