White Industries fixed gear cogs utilize a proprietary spline system in place of the standard thread-on cog system that locates the cog on the White Industries Track and ENO hubs.  This allows pedaling forces on the cog to be carried by the spline as opposed to threads.  No threads means no stripped cogs or hubs!  Made from heat treated, electroless-nickel plated 8620 steel, they are super-tough. These cogs will not fit on any other brand of hubs except White Industries Track and ENO hubs and Rolf P-Town hubs.