A cutting tool assembly, comprising: a shank including an insert pocket formed from a top and having a base wall, a lever receiving portion formed downwardly from the base wall, and a screw hole disposed perpendicularly to the base wall and formed upwardly from a bottom of the shank; a cutting insert having a rhombus shape; a clamping lever received in the lever receiving portion, the clamping lever including a first extension portion disposed perpendicularly to the base wall of the insert pocket and a second extension portion extending from a lower end of the first extension portion parallel to the base wall of the insert pocket; and a set screw fastened to the screw hole, wherein a portion of the set screw overlaps with a portion of the cutting insert when the shank is viewed from top, wherein the set screw is fastened to the screw hole formed upwardly from the bottom of the shank, and wherein the cutting tool assembly further comprises: a shim disposed on the base wall of the insert pocket and including a shim bore extending through centers of an upper surface and a lower surface of the shim, wherein the cutting insert is disposed on the upper surface of the shim, the cutting insert including an upper surface, a lower surface, a plurality of side surfaces located between the upper surface and the lower surface of the cutting Insert, and an insert bore extending through centers of the upper surface and the lower surface of the cutting insert, characterised in that, the set screw includes a screw head located upward, a threaded portion located downward, an engaging groove located between the screw head and the threaded portion and engaging a front end of the second extension portion, and wherein the shim includes an avoiding portion configured to avoid an interference with the screw head. a shank including an insert pocket formed from a top and having a base wall, a lever receiving portion formed downwardly from the base wall, and a screw hole disposed perpendicularly to the base wall and formed upwardly from a bottom of the shank; a cutting insert having a rhombus shape; a clamping lever received in the lever receiving portion, the clamping lever including a first extension portion disposed perpendicularly to the base wall of the insert pocket and a second extension portion extending from a lower end of the first extension portion parallel to the base wall of the insert pocket; and a set screw fastened to the screw hole, wherein a portion of the set screw overlaps with a portion of the cutting insert when the shank is viewed from top, wherein the set screw is fastened to the screw hole formed upwardly from the bottom of the shank, and wherein the cutting tool assembly further comprises: a shim disposed on the base wall of the insert pocket and including a shim bore extending through centers of an upper surface and a lower surface of the shim, wherein the cutting insert is disposed on the upper surface of the shim, the cutting insert including an upper surface, a lower surface, a plurality of side surfaces located between the upper surface and the lower surface of the cutting Insert, and an insert bore extending through centers of the upper surface and the lower surface of the cutting insert, characterised in that, the set screw includes a screw head located upward, a threaded portion located downward, an engaging groove located between the screw head and the threaded portion and engaging a front end of the second extension portion, and wherein the shim includes an avoiding portion configured to avoid an interference with the screw head.