Tap and feed trimmer head (7mm, left hand thread, male). The model which we recommended to use are C220, C2510, T220, T230S, SBA-TX24, 22C, C230 and T230XR. SRM-220ES, SRM-265ES, SRM-300, SRMF-340, SRM-510ES In addition to the models, as long as the gear shaft is 7 mm and counter-clockwise rotation