When the GT6 was developed from the original Triumph Spitfire the brakes were uprated to take the extra power and weight, the discs from Girling Type 14 to Type 16, and the rear drums from 7" x 1.25" to 8" x 1.25" (later Mk3 to 7" x 1.50").

Disc brakes were first patented by Lanchester in 1902.  However it was Dunlop (with the help of Jaguar 1950s racing cars) who can properly be credited with the design and development of the first viable disc braking system for road and racing cars. In the 1960s Girling acquired the brake interests of Dunlop. Later, Girling became part of Lucas Industries.

Girling Type Part Number Model Pots Piston Dia. Piston Height Piston Groove Pad Area Bolt Dia. Caliper bolt spacing Bolt part number
14 516212 Spitfire Mk3, IV & 1500 2 48mm 29mm       3.25"  
16P 510792 GT6 Mk 1 2 54mm 29mm 1.5mm   7/16" Diameter UNF thread x 1"3/8 Long 3.5"  
16PB 157685 GT6 Mk 2 2 54mm 29mm 3.4mm   7/16" Diameter UNF thread x 1"3/8 Long 3.5"  
16PB (Metric) 158713 GR6 Mk3 2 54mm 29mm 3.4mm   M12 x 35mm 3.5"