I modified this jig so I could use a hex driver without a set screw. I also felt that circle was too big for my needs with my mini so I made it into a quarter and made the hole to fit the hex driver.   Typically my bed level is adjustment is <90 degrees so the quarter circle suits my needs quite well and fits better on the edges of the bed. 

You will need to ream out the hole a bit on the quarter circle to make it fit. The hex on the arrow will be a tight friction fit.