Update: this thing fell apart rather quickly. If you decide to try this, either use something stronger than epoxy putty to hold the "threaded screws" (I still haven't found out the proper English term) together or find another way basing on the same general principle. I might write another instructable on the subject matter some time.
In this Instructable I will show you one way to build a simple tool that will help you to install, remove or re-install bridge mounting posts for Tune-O-Matic style bridges that go directly into the top wood of an electric guitar.
This particular tool is inspired by the Tune-O-Medic Post Tool that is available for purchase at Stewart-MacDonald for $22.95. However, I'm cheap, have no credit card and live in Germany, so apart from not being able to buy/mail-order it in the first place, shipping and taxes would greatly increase the price I'd have to pay for this simple tool.
I'm slowly building up a collection of specialised tools, home-made ones as well as actual professional tools and I figured it wouldn't hurt sharing some information and experience along the way.
There are, of course, much more simple and most likely cheaper ways of achieving this using the same principle as this tool. I'm going to give you alternative ways of building such a tool at the end of this instructable.
A little bit of background:
On some older electric guitars (as well as some replicas, reissues, copies/knock-offs), the bridge is connected to the body via two threaded posts that are screwed directly into the top of the guitar. The bridge itself rests on two knurled nuts that allow for the height of the bridge to be adjusted. (See first picture) Modern bridge designs, as well as 'stop' tail-pieces, use bushings that are installed in the top of the guitar. These are knurled on the outside and threaded on the inside to accept the post. (See second picture)
If you want to refinish your instrument or install a newer bridge that has poles that require threaded bushings, you will obviously want to remove these posts.
To my knowledge, this type of bridge, the so-called Tune-O-Matic bridge, was introduced by Gibson with their Les Paul model solid body electric guitar in the mid 1950s.
Also, other stringed instruments with arched tops such as mandolins, bouzoukis and hollow-body electric/acoustic guitars with arched tops and backs (aka jazz guitars) use a similar way of installing the bridge. With these, the bridge (often a adjustable Tune-O-Matic style bridge or a compensated wooden bridge) rests upon a wooden base that is scalloped on the underside to fit the arched top.