Crank bolt and top-cap ruler centering tool

Stick this in your 10mm hex bolt in your bottom bracket, and use the slot to hold your tape measure while you measure out different positions on your bike.

Added similar tools to put in steer tube top cap and older Campy and Shimano bottom bracket bolts.

Latest update puts size of the hex end on the top with the ruler slot.

See: http://www.thingiverse.com/thing:1858794 for a holder to put them all in and even screw or hang them on the wall of your shop.