I did some research. looks like it is for banjo neck adjustment. it controls the neck up-down angle when you lay your banjo flat. You can use a flashlight to see where the hole leads to. as long as the neck is not moving and not affect playing, I don't worry too much about it...
@@dododepapa Thank you. Unfortunately for me it is affecting playing. I will have to try and find out what the missing piece looks like and try to find or make one. 😊
