Mission Brewery cap on a sample bottlecap knob Beer Cap Knobs on Cherry SG Lefty Volume/Tone Knob - A volume/tone knob for guitar... endlessly customizable because you add the last component - your favorite beer or soda bottle cap. The knob is shaped so that caps can be pressed on and fit snugly. This model is for 6MM potentiometer shafts and has 6 ridges in the shaft opening to fit snugly on coarse-splined, fine-splined or smooth shafts.  These have been used on Gibson, Epiphone and Squier guitars so far with no problems, but please double-check your potentiometer shaft size before ordering. If there's a demand for 1/4" shafts I'll post an alternative version of this knob.

Beer Cap Cabinet Knob Cabinet Knob - The Bottlecap Cabinet Knob is for dressing up cabinet doors and drawers with bottle caps to give them a custom, rustic look.  These knobs will need additional hardware for fastening them to cabinets or drawer faces.  For cabinet faces with a 3/4 inch thickness, you'll want to use 8-32 x 2" screws with a shallow head (they're called 'truss combo' screws).  For drawers with a 1-1/4 inch thickness (3/4" face + 1/2" drawer front), use 8-32 x 2-1/2" screws.  Links to the same hardware that I use in my own cabinet knobs are below.

Available to buy at Shapeways.com
Gentle Bottle Opener How To Get A Good, Clean Bottlecap - In most cases a bottlecap will get bent or scratched when you use a regular bottle opener.  Sometimes you can set one face-down on a hard surface and press down on the inside to bend it back straight.  What I suggest if you're popping a cap that you specifically want to keep straight and unscratched is to use some sort of padding on the opener.  The image to the left is the one in my office - it's just got a paper towel wrapped around the part that presses against the top of the cap.  Then, instead of popping the cap all in one motion, just apply enough pressure to bend the tabs on the cap slightly - then move around the cap to a new spot and do it again.  Usually it takes no more than three or four spots before the cap comes off with no bends or scratches.

Placing/Replacing Caps on the Knobs - The tops of these knobs are sized so that a bottlecap from a glass beer or soda bottle should snap down and fit snugly.  The best way I've found to do this is to set the knob on a hard surface, place the cap on top and then press down hard with the palm of your hand.  If the cap is too tight you can stretch it out slightly, and if it's loose you can squeeze the sides of the cap in once it's in place.  Glue or epoxy on the inside of the cap is an option, but so far I haven't had to go that far.  If your cap gets worn or you just want a different look from time to time, always pull the knob back off of an instrument or furniture before removing and replacing a cap.  The stress of popping a bottlecap off while the knob is in place can damage a potentiometer shaft or nick wood finishes.

Swapping Out Instrument Knobs - Modifications done by yourself are (of course) done at your own risk, but changing instrument knobs can be a simple job.  One important thing to remember is that knobs can fit very tightly on volume/tone pots, and it can be really easy to dent or chip your finish if you aren't careful.  Knobs should come off fairly easily if they're pulled directly upward.  My suggestion would be to pick up a knob-puller if you'll be switching out knobs regularly.  The 6mm hole in these knobs has small ridges in it to fit either coarse- or fine-splined shafts.  In case there's any looseness on a smooth shafted pot or after placing/removing it a few times, I added a side shaft sized to fit 6-32 x 1/4 set screws.  The hole should be just the right size for one of these screws to self-tap (I've done it with no problems), but if you happen to have a 6-32 tap in your toolbox tapping the hole first makes for a perfect fit.