A method and apparatus for clamping an electrode tube in an EDM drill equipment is incorporated with an elastic seal and a collet. The method providing an insert having a through hole disposed at the center to concentrically accommodate and restrict the elastic seal, placing the insert into the collet, and inserting the electrode tube in the insert and the elastic seal, tightening the nut to the spindle to clamp the electrode tube and passing the EDM machining current from the spindle to electrode tube. The apparatus includes an insert having a retaining ring to restrict an elastic seal, a through hole to admit insertion by the electrode tube. The insert of the above method and apparatus comprises a guiding pipe to be secured in the collet, and a tapered guide hole interconnecting with the through hole to facilitate insertion of the electrode tube. Optional slots are provided at the lower portion of the guiding pipe.