any of you have any recommendations for the best type to drill bit to drill a small hole in a shell for jewelery purposes?
Stew-Mac sells parts for Guitars, they might know or have the type of drill.
http://www.stewmac.com/
Keep the drill speed down, heat can cause the shell to crack. Having someone squirt it with water while you are drilling helps keep it cool.
Make sure not to inhale fumes from shell or get the dust in your eyes, I’ve heard that it’s toxic.
You can also check out Music Instrument Makers Forum: http://www.mimf.com/
If you’re referring to drilling sea-shells for oil I think you’ll have to fight the EPA.
carbide bits, but I have even used a tile bit, but that needs a little more finesse and can’t do long holes.
Masonry bits.
djm
What are masonry bits? 
I will not bide by this! Nor will I bide by my car!
Masonry bits are drill bits designed specifically for drilling into masonry. They is what they be.
djm
Yup! Carbide tipped!
carbide tipped, are those the gold colored ones? I also have a set of tiny diamond grinders that might work or help, i think I’ll try some test runs on several before i do the one i want.
DUUHH
I use solid carbide drill bits and router bits for shell and stone work. Carbide tipped drills often have an applied tip to a plain steel bit. I am not sure what sizes them come in as I am mostly familiar with the masonry type in that style. Solid carbide bits come in many sizes from micro on up for use in moto-tools up to drill presses. Most of my work is with stearite, slate, catlinite, with shell inlay. Colour-wise carbide are usually just shiny steel. Titanium nitride, gold coloured, is often used on HSS bits to make them more durable?
Diamond should work well, I use circular and jigsaw diamond blades for cutting large chunks of stone and also use some micro-ruby grinders for finer work.
Um … then why did you ask what’s a masonry bit?
djm
Snails use their tongues. This however would take a long time with a human tongue. Know any snails?
Doc
Um…then why did you say masonry bit after I said carbide bit?
Lots of drill bits have carbide on the tips (wood, steel, etc.), but a masonry bit is especially shaped for specifically cutting into cement or concrete. You wouldn’t use a carbide-tipped wood drill on concrete.
djm
Yes, you can use a carbide-tipped wood drill bit on concrete, maybe not a brad point. I"ve used carbide-tipped wood drill bit to plunge through 8" of stone, no problem, no damage to the bit. Solid carbide makes a nicer hole.
I think it needs to be a small one.
Better your drills than mine.
This is why I do not loan out my tools.
djm
May I borrow your bow-saw? Ike did a lot of damage to my forest here.
Real men use chainsaws.
Why? Bowsaw is more work. Chainsaw’s the easy way.
Also, I’d run out of fuel before finishing.