This is the highest quality set of original sized brake rotors available for your Triumph TR3B through TR6. 
Produced by one of the largest automobile parts manufacturers in the world -  TRW -  from high quality OEM grade cast iron.  The rotors also have a beautiful finely cut non-directional surface finish, which is critical for for the first few hundred miles of brake rotor and brake pad wear.  The brake rotors also feature directional  slots and cross drillings that increase braking efficiency by venting the gases that develop under the pad surface during hard braking.
Rotors are sold as a matched pair (left and right) due to directionality of the venting slots and cross drillings.