Schaller 3D-4CH Octave Adjustment Screw Old-style minus head. Current models have been changed from minus head to hexagon head. The wrench size specification is unknown, whether it's metric or inch. This is the old-style minus head. For those whose octave adjustment range on the 3rd/4th string is insufficient, the fixing position for the +5mm saddle will be deeper. For those whose saddle fixing position is less than 2 turns of the screw, you can achieve the correct sound by installing a longer screw. ※ Although it is new and unused, it has been opened for photography. If you are interested, how about this opportunity? I'm waiting for you.