GTX or GSX series Actuators incorporate a servomotor built around a roller screw element. This gives a very compact design which can directly replace pneumatic and hydraulic cylinders in many applications. GSX is a heavy duty model, the GSM is for standard duty.
FTX or KX series Actuators are based on a roller screw driven by an external servomotor. They are often the best choice where applications require the highest dynamic performance. The FT series is for heavy duty cycles, K series for standard.