During the course of an airplane building project, you might come across a task where you need to precisely match-drill a hole—a simple operation when the part with the existing hole is on top of the undrilled piece. But when the order is reversed, it gets tricky. You could do it with some masking tape folded over itself, but that’s not very precise. A strap hole duplicator is a tool that’s really handy and inexpensive, and it makes the task a breeze.
One tang has a pin that fits in the existing hole, and the other tang is fitted with a drill bushing. Place the pin in the hole you want to match, slide the undrilled piece into position over it, and drill through the bushing.
A set of 6-inch duplicators costs about $40 at Yardstore.com.
This was not the tool I was looking for, but is absolutely the tool I needed.
Great recommendation!
Just used mine recently, but I forgot that you need to have all the holes on a piece located before drilling, otherwise the angle created by using one, throws off the location, then its a mess. You need a bunch