I watched this run in person, the spring is there as a timing spring to keep the armature bar pivoting up and down as the horizontal cam in the back... (i guess you could call it a cam?) drives the bar as it as it spins. confused yet? it even looks confused when it runs. The contact screw is just to keep the spring holding its tension making sure the armature bar snaps back into position. Fun to watch the guy said they have tattooed with it before but it was not for sale just made it cause he could.