These are spare parts for HDX500SAH which using Hitec cyclic servos. Note that if the Part Name is ended with HDX500SAH/S, it is compatible with both HDX500SAH and HDX500SAS. If Part Name is ended with HDX500SAH it is only for HDX500SAH helicopters and if Part Name is ended with HDX500SAS, it is only for HDX500SAS helicopters.