Device for holding a cutting insert in the pocket of a tool holder

In a tool holder for supporting an insert with a central hole therein, said tool holder having a pocket comprised of a bottom wall and side wall for seating the insert therein, a hole formed downwardly through said bottom wall and having the axis offset towards said side wall from the axis of said central hole of the insert, when said insert is seated in said pocket, a pin member having a head on one end adapted to engage the insert from above and the other end threaded and adapted for extending downwardly through the central hole in the insert and said hole formed downwardly in said bottom wall in said tool holder, and a nut threadedly engaged with said other end of said pin member and adapted to abut a lower side of said tool holder to clamp the insert in said seated position, the improvement which comprises a counterbore formed in at least one of the opposing faces of said nut and said holder, said counterbore formed coaxial with said hole in said bottom wall, spring means seated in the counterbore and in unstressed condition projecting axially outwardly from the mouth of the counterbore, said nut compressing said spring means and abutting the bottom of the holder when the pin member is tightened in the nut.