One side for single freewheel and one side for fixed gear.

The hub can be used for multiple mounting dimensions thanks to the supplied spacers.

Specifications of the rear hub:
Brand: Sturmey Archer
Model: HBT30-F Flip-Flop
Color: Gold
Number of spoke holes: 36GTS
Type of brake: Rim brake
Number of gears: 1S
Type of axle: Fixed axle 174 MM
Axle included: Yes, with nuts
Type of bearings: Industrial bearings
Average weight (GR): 301
Intended use: Fixy - Singlespeed

Data for spoke length calculations using the Sapim spoke size calculator:
Total length of the hub (MM):130 - 120 MM
Non-gear side (MM): 31
Gear side (MM): 31
Hub diameter non-gear side (MM): 61
Hub diameter gear side (MM): 61

Link to spoke calculator: