A metal cutting tool has a supporting tool, which has a recess for accommodating a cutting plate. The cutting plate is provided with a clamping trough, which is held in the supporting tool by a clamping claw. The clamping claw is fixed against the supporting tool by a clamping screw. A pressure piece is placed on the clamping claw and its underside facing the cutting plate is provided with a cam, which is in contact with the clamping trough and the clamping claw pulls the pressure piece toward the clamping screw.

A holder for grooving work includes a shank portion, and a head portion located on an end portion thereof. The head portion includes an insert attaching space, an upper and lower respectively located above and below the insert attaching space, a slit extending backward from the insert attaching space, an upper and a lower jaw connecting portions divided by the slit, an upper clamp surface on the upper jaw and a lower clamp surface on the lower jaw opposed to the insert attaching space. A column-shaped groove is connected to the deepest end of the slit. The column-shaped groove is formed to reduce the thickness of the upper jaw connecting portion, and extends from the lateral face on the side of the insert attaching space halfway along the deepest end of the slit toward the opposite lateral face. Upon attaching the insert to the holder the cutting tool is obtained.