there are 3 sears comercially available from apex. the standard hard sear and 45/shield hard sear. improved geometry for cleaner break etc compatable with the stock trigger and the apex AEK trigger shoes
then the FSS sear which pushes the break point further forward and then the FSS trigger or FF trigger shoes have overtravel stops built in. therefore reducing the overall trigger travel. these need the fss or FF trigger shoes to work correctly