This is the original style headlamp bulb holder. RPI offers a chrome bulb holder for these models. Look up part# RD3936BLBSCK 1945-1955 Silver Wraith, Mk-6, R-type, Silver Dawn  

This is the bulb holder for the luggage compartment 1946-1955 Bentley MkVI & R Type, RR Silver Dawn & Silver Wraith 

This is the bulb holder for the rear lamp. Late Silver Cloud II, III (after SAE389) Phantom V (after 5LCG 19) Bentley S-2,3 (after B142DW)

This is the Bulb Holder. 1980-1989 Eight, Mulsanne, Spirit, Spur, Turbo (VIN 8862-27779)  

This is the bulb for the rear stop lights. All models from 1945 onward