MT2 shank with MT4 hole. Morse Taper extension socket. We also have Extension Socket for MT1-MT2, MT2-1MT, MT2-2MT, MT2-3MT, Mt2-4MT, MT3-1MT, MT3-2MT, MT3-3MT, MT3-4MT, MT3-5MT, MT4-2MT, MT4-3MT, MT4-4MT, MT4-5MT, MT5-3MT, MT5-4MT, MT5-5MT, MT6-4MT, and MT6-5MT.
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