The following codes of Bosch Sparkplugs I found on the internet:
R : Resistor plug
C : Copper Core
P : Platinum Core
T : Triple tip
W : 14mm Threads
D : 3/4" Thread reach with extended tip
P-4 : Platinum 4 tip
The BMW Twin uses Bosch W6DC spark plugs what means they have
14mm Threads, the temperature range has code 6, 3/4" Thread length and a copper core.