Specifications of the rear hub: 
Brand: Sturmey Archer
Model: SX-RK3
Color: Silver
Number of spoke holes: 36GTS
Type of brake: Disc (6 bolts)
Number of gears: 3S
Type of axle: Fixed axle 216 MM
Axle included: Yes, with nuts
Type of bearings: Ball bearings
Average weight (GR): 1414
Intended use: City
 
Data for spoke length calculations using the Sapim spoke size calculator: 
Total length of the hub (MM): 170
Non-gear side (MM): 40
Gear side (MM): 32
Hub diameter non-gear side (MM): 91
Hub diameter gear side (MM): 91
 
Link to spoke calculator: www.sapim.be/spoke-calculator