A tool holder having a holder body, an opening of the holder body having opposing upper and lower jaws respectively defining upper and lower pocket surfaces of an insert receiving pocket, and a resilience slot extending away from the insert receiving pocket. A first plane intersects the upper and lower pocket surfaces, and an actuating member extends from the upper jaw along a first axis in a downward direction and traverses the resilience slot. The lower jaw includes an access bore, and a locking member occupies the access bore and engages a locking portion of the actuating member. The upper jaw has a top jaw surface facing in an upward direction, and the first axis intersects the top jaw surface. A cutting tool is configured with the tool holder and a cutting insert removably secured in the insert receiving pocket.

A polygonal cutting blade having a circular arc-shaped groove in a hole includes a blade body composed of an upper surface, a lower surface and a plurality of main side surfaces connecting the upper surface and the lower surface. The blade body has a central hole penetrating through the upper surface and the lower surface, and is centrally symmetrical about a central axis of the central hole. At least one set of positioning side surface comprised of adjacent two of the main side surfaces is provided. An inner surface of the central hole has at least one circular arc-shaped groove fitting with a fastening screw for fixing the cutting blade. The circular arc-shaped groove directly faces toward an intersection of the two main side surfaces of the set of positioning side surface. A groove central axis of the circular arc-shaped groove has an offset distance from the central axis.

A polygonal cutting blade having a circular arc-shaped groove in a hole includes a blade body composed of an upper surface, a lower surface and a plurality of main side surfaces connecting the upper surface and the lower surface. The blade body has a central hole penetrating through the upper surface and the lower surface, and is centrally symmetrical about a central axis of the central hole. At least one set of positioning side surface comprised of adjacent two of the main side surfaces is provided. An inner surface of the central hole has at least one circular arc-shaped groove fitting with a fastening screw for fixing the cutting blade. The circular arc-shaped groove directly faces toward an intersection of the two main side surfaces of the set of positioning side surface. A groove central axis of the circular arc-shaped groove has an offset distance from the central axis.