Centerline-Tool

This tool helps to find the center of cylindrical objects.
Imagine you cut a broomstick and want to drill a hole lengthwise, in center.

Place the tool on the end, so that the two sides touch the circumfere.
The slide a pencil along the slot.
Rotate the tool by some amount (ca 90° will do fine)
Slide the pencil along the slot again.
Remove the tool.
Where the two lines intersect is your center.

Best printed upside down. No support needed.