Do you have 4mm screws and bolts that you need to adjust somewhat frequently but don't want to carry around an hex key with you? This is the make for you! This super simple design can be printed in mere minutes and can be screwed onto any 4mm bolt to allow you to adjust the bolt with your fingers. 

The head is designed to be threaded with the bolt, which may take some time and force. However, this ensures that the head has a strong connection to the bolt and can be turned reliably in both directions without unthreading the head of the thumbscrew.