This Instructable shows the basic steps of how to attach an old and beat up found-by-the-side-of-the-road oil cap onto a cheap belt buckle.

This buckle is a great visual pleaser, plus it makes a great gift for geeks and gear-heads alike.

Step 1: Materials

You need:

A belt buckle: I used the simple flip-open kind, as you will see in the pictures.These are common and can be found in most accessory stores, they are intended for cloth belts.
A belt that fits the buckle.
A small screw: available anywhere screws are sold/bartered/found.
An oil cap: Easier to find than you might think. Ask around, you can probably get one for free. Mechanics shops probably have a whole box of them just lying around the shop, and a junkyard would be sure to have one. Or, you could search the side of the road until you get lucky. If all else fails, you can take one from your roommates/spouses/younger siblings/boss's car. (use discretion)

Note: My oil cap was plastic, so I just used a screw to attach it. Your cap could be metal, or both metal and plastic. It is kind of open-ended how you attach it, but epoxy or other things would great too.

Step 2: Tools

For this build, I used

A power drill, with a 1/16 drill bit
A craft knife
A Dremel rotary tool
Safety goggles
A wrench that fit the screw I was using
Cleaner and sand paper for cleaning up the grimy oil cap
Paint pen

Step 3: Clean Up the Cap

The oil cap I had was covered in road grime and oil residue. I cleaned off the worst of it with an old toothbrush and some heavy duty cleaner

Step 4: Trim Off the Extra Bits

The cap I used had a threaded part on the back that was all shredded and prevented me from attaching it easily. Using a craft knife and a Dremel tool, I carved all of it off, leaving the back of the cap flat.

Step 5: A Light Sanding and Some Paint

There were still some grimy spots on the cap that would not come out with washing, so I sanded them lightly until they were gone.

I noticed that the "oil logo" in the center didn't show up very well at a distance, so I went over it lightly with a black paint pen, and it helped the over all look tremendously.

Step 6: Measure the Cap and the Buckle

I had to make sure that when I attached the cap to the buckle, it would not interfere with the movement and closing of the buckle. Basically, I held the two parts together, and flipped the buckle around until I found a spot that let me mount it easily and did not interfere with the buckle. I then marked it for reference.

Step 7: Drilling and Screwing

I drilled a hole in both the buckle and the cap. The hole In the cap did not go all the way through, but was just deep enough that the screw i had would fit.

I used the to put in the screw, and then I was effectively done!

Step 8: Done! Wear With Pride!

Tada! you just created an awesome belt buckle! Enjoy. Branch out, you never know what random things can be attached to old buckles to make them AWESOME!