the following specs are from a 1964 data book on all makes of m/cycle ,here is Douglas
all models 1927-39
BRAKES F&Rear dia 8inch length 23 inch, width 1 inch, thickness 3/16, ferodo ref no DG/1/1 type of lining BA,, box rivets 13/C3
Clutch all models 1934/37
dia 6.3/4 inch bore 5 inch thickness 1/8 ferodo ref no 2/DG/2 ferodo type RAD11 rivets ref 12/C15
I have ref for other machines if you want them
