Rollers are the wear item that sets bolt gap on a roller-delayed gun, and bolt gap is what decides whether a JP-5 cycles. This kit carries the -2 size: rollers two sizes under standard, for bringing an over-tight bolt gap back into spec.
JP machines the rollers from a proprietary bearing steel and finishes them to outlast the aftermarket rollers sold for MP5-pattern guns. Each kit has two rollers, a roller retainer spring, and the spring pin, so one kit does one bolt head.
One thing to know: the rollers fit the H&K MP5, but JP says the roller retainer spring in the kit does not. Clones should be checked for H&K-standard parts. And the size is not a guess: measure bolt gap first with the gauge set, swap, then measure again, because the whole point of a roller change is landing inside JP’s gap window.
The trade-off is that buying the wrong size solves nothing. A shooter who does not know the current gap should start with the gauge set, not the rollers.
