It is the bolt that goes through the neck to attach the kahler locknuts to the headstock.

Length: 0.0000 in
Width: 0.0000 in
Height: 0.0000 in
Weight: 0.300 oz
Packaging: 0.0000 kg
Units in box: 1
Parts by Make/Model > Kahler Parts > Locknuts
Parts by Type > Mounting Hardware
Parts by Type > Locknuts and Stringlocks > Locknut and Stringlock Hardware