Kluson Roundbacks CTM LOCKHEAD, 6-R

This is how the Kluson Lockhead system works: First you have to pull the string through the hole in the shaft until the string lies tightly on the frets. When you tighten the upper cylinder counterclockwise with a coin (5 euro cents), a small pin inside the shaft tightens the string. Now you can start tuning.
All Kluson lockheads have one ingenious point: you can't unscrew the shaft's cylinder because it ends up in an open loop. That means the cylinder can't fall off and get lost!