Box One Single-Speed Aluminum Cogs are 7075-T6 aluminium alloy.
It's designed to fit Shimano™ compatible cassette hubs and has a 5mm wide inner base, giving a more solid interface with the cassette body. The alloy cogs are anodised black with laser-etched graphics.
 
SPECIFICATIONS:
Material: CNC-Machined 7075-T6 Aluminium
Finish: Two-Toned & Solid Anodized w/Laser-Etched Graphics
Size: 13T, 14T, 15T, 16T, 17T, 18T
Fit: 5mm wide base for more solid interface with  HG Freehub Body
Chain pitch: 3/32” or 1/8”