We seen this concept from several brands, but Charge has a bolt on fixed hub as well: the Shaker!

Exclusive Charge design fixed gear specific rear hub and cog. 4 bolt fixing cog prevents stripped lock ring threads. Lightweight large flange design with 120mm spacing, smooth running Japanese bearings and bolt on hollow axle. 15t,16t,17t and 18t cog sizes available.

Seen on the Charge website.