A cutter holder has a holder, a collet, and a nut. The holder has a first threaded portion having an external thread, a first abutting surface, a second abutting surface, at least one recess, and at least one sealing member. The at least one recess is recessed in the second abutting surface. The at least one sealing member is mounted in the at least one recess and partially protrudes from the second abutting surface. The nut has a second threaded portion having an internal thread, a third abutting surface, and a fourth abutting surface. The internal thread and the external thread are corresponding internal and external trapezoidal threads, respectively. The third abutting surface and the first abutting surface have a corresponding diameter with a clearance therebetween being less than 0.015 millimeter. The fourth abutting surface and the at least one sealing member are in an interference fit.

A cutter holder has a holder, a collet, and a nut. The holder has a first threaded portion having an external thread, a first abutting surface, a second abutting surface, at least one recess, and at least one sealing member. The at least one recess is recessed in the second abutting surface. The at least one sealing member is mounted in the at least one recess and partially protrudes from the second abutting surface. The nut has a second threaded portion having an internal thread, a third abutting surface, and a fourth abutting surface. The internal thread and the external thread are corresponding internal and external trapezoidal threads, respectively. The third abutting surface and the first abutting surface have a corresponding diameter with a clearance therebetween being less than 0.015 millimeter. The fourth abutting surface and the at least one sealing member are in an interference fit.

Intrusion of chips is prevent into gaps formed between inner end surfaces of master jaws and a chuck cover. A top plate is disposed at the center of an end surface of a chuck body. Top covers, which move in conjunction with movements of master jaws when opening and closing the chuck, are disposed in top cover guide recesses formed at three positions on the top plate. Each top cover abuts the center-side end parts of serrated surfaces formed on both widthwise sides of a respective master jaw and the center-side end part of a step section of a stepped claw therebetween, and the top covers close gaps formed at the center-side end parts by the movements of the master jaws at all times by moving in conjunction with movement of the master jaws.

A hydraulic chuck includes a chuck body, a fixed seat, a rotary seat and a plurality of flexible seal members. The fixed seat is fixedly mounted to the chuck body. The rotary seat is rotatably mounted to the fixed seat and cooperates with the fixed seat to define a gap therebetween. Each of the seal members has a first annular segment fixedly mounted to the fixed seat, a neck segment extending from the first annular segment and through the gap, and a second annular segment connected to an end of the neck segment distal from the first annular segment, and disposed adjacent to the rotary seat.

A hydraulic chuck includes a chuck body, a fixed seat, a rotary seat and a plurality of flexible seal members. The fixed seat is fixedly mounted to the chuck body. The rotary seat is rotatably mounted to the fixed seat and cooperates with the fixed seat, to define a gap therebetween. Each of the seal members has a first annular segment fixedly mounted to the fixed seat, a neck segment extending from the first annular segment and through the gap, and a second annular segment connected to an end of the neck segment distal from the first annular segment, and disposed adjacent to the rotary seat.

A cutter holder has a body, a fastening bolt, and a vibration absorbing structure. The body has a specific weight. The fastening bolt is mounted inside the body. The vibration absorbing structure is mounted inside the body and has a sleeve, an elastic unit, a spacer, and a set nut. The sleeve is mounted around the fastening bolt and has a specific weight. The specific weight of the sleeve is larger than the specific weight of the body. The elastic unit is mounted around the fastening bolt and has two opposite ends. One of the ends of the elastic unit abuts against the sleeve. The spacer is mounted around the fastening bolt and abuts against the other end of the elastic unit. The set nut is screwed with the fastening bolt and abuts against the spacer.

A cutter holder has a body, a fastening bolt, and a vibration absorbing structure. The body has a specific weight. The fastening bolt is mounted inside the body. The vibration absorbing structure is mounted inside the body and has a sleeve, an elastic unit, a spacer, and a set nut. The sleeve is mounted around the fastening bolt and has a specific weight. The specific weight of the sleeve is larger than the specific weight of the body. The elastic unit is mounted around the fastening bolt and has two opposite ends. One of the ends of the elastic unit abuts against the sleeve. The spacer is mounted around the fastening bolt and abuts against the other end of the elastic unit. The set nut is screwed with the fastening bolt and abuts against the spacer.