A plus sign is good enough, 4 pieces, top bottom, left, right. An yeah, tighten till it just grips the matchbook to hold it. An should again, slide out easily, with just a little pull.
I also learned that is the separation to set the dwell on an old kaw 1100 or wtf size it was. I just knew I could barley hold it up one legged with a tiny gal on the back, and I could hit 140 mph with her screaming the cops are chasing us, in like a no time flat. lol. But Grandpa Crystal showed us all kinds of cool aviation mechanic tricks.