Abstract: A linear movement tuning key for the peg head of a stringed musical instrument. A key includes a generally cylindrical body portion having a radially extending flange at the upper end, upon which is mounted a guide roller having its axis generally coplanar with the body of an instrument string. The roller is adapted for receiving the string thereacross and rotating therewith for direct orthogonal transfer of string tensioning forces. A tuning piston is mounted within a central axial opening in the cylindrical body portion of the key with the lower inner portion of the axial opening being threaded to receive a screw actuation ram. The lower, outer portion of the key body is also threaded to receive a cylindrical mounting sleeve, the upper edge of bears against the under surface of the peg head to rigidly secure the key body portion within the peg head.