His link is a 3-speed flywheel.
3 Speeds Bicycle Freewheel Sprocket 16T-19T-22T Bike Flywheel 3 Gears For Regular Bike #410 Chain Convert Single Gear To 3 Gears
34MM Single Speed Bicycle Freewheel Sprocket Part Gear Bike 16T 18T 20T 22T 24T
16T 18T 20T 22T 24T 34MM Single Speed Bicycle Freewheel Sprocket Part Gear Bike
Cycling Bicycle Freewheel Part MTB Road Bike Cassette Sprockets Freewheel Cog
Hycline Single Speed Bicycle Freewheel 16T, Bike Freewheel
Hycline Single Speed Bicycle Freewheel 16T, Bike Freewheel-BLACK
