Vintage Style String Trees used on Fenders mostly or Headstocks with a straighter angle needing the extra tension to stop string slippage off the nut.
Screw length: 11mm
for BEST results use the right size drill bit if going into a NEW Headstock. These are small screws and forcing them into a smaller diameter hole will result in stripping the screw head. Having a perfect size hole will result in a perfect fit. I've done this enough times to know.