Because most people usually overtighten their axle nuts like uncivilized gorillas, these little bastards break all the time on Formula hubs. Replace 'em and keep a few extras on hand just in case human restraint ain't your thing.

These will work on other track hubs too but you may need to get creative with some axle spacers.

Sold in pairs.

FYI: Formula updated the outer diameter of the M10 lock nuts for rear hubs, so they may not match the ones you are replacing. The smaller diameter helps to prevent them from breaking.