Specifications of the rear hub: 
Brand: Sturmey Archer
Model: RS-RK3
Color: Zilver
Number of spoke holes: 36GTS
Type of brake: Disc (6 bolts)
Number of gears: 3S
Type of axle: Vaste as 185 MM
Axle included: Yes, with nuts
Type of bearings: Ball bearings
Average weight (GR): 1069
Intended use: City
 
Data for spoke length calculations using the Sapim spoke size calculator: 
Total length of the hub (MM): 135
Non-gear side (MM): 36
Gear side (MM): 46
Hub diameter non-gear side (MM): 66
Hub diameter gear side (MM): 66
 
Link to spoke calculator: www.sapim.be/spoke-calculator