Indexing Capper Cap Feeders specification should start with the real closure.
Indexing capping machines need cap delivery to happen at the right point in the machine cycle. The feeder may need an escapement, cap present sensor or control link to release each cap at the correct time.
For a better buying decision, the useful comparison is not only hopper size or headline speed. It is how the feeder behaves with your closure, how the capper receives the cap and how easy the line is to run after changeover.
The safest specification route is to start with real closures, target output, line photos and the exact point where the cap must be presented. That avoids choosing a feeder on a generic speed figure that does not match the cap or capper.