Jenny,

Not an easy answer without a few facts:

Simply put, the faster the better, I use an NSK, 300,000 RPM. I tried piercing with a Foredom +- 15,000 RPM but was not satisfied with the results.

On the NSK, I use the 699L bits.

If you know who the manufacturer of the tool is, you can check out the specs as far as RPM & bit size.

Treeline USA is a good source for bits etc. Multimedia File Viewing and Clickable Links are available for Registered Members only!!  You need to or

I'm sure others will be chiming in as well.

Good luck, piercing is a fun way to enhance your projects. 

Since I have been piercing for years I'll throw my two cents in here also but like others have said there are many factors that apply here. The number one thing to consider is how thin can you turn. If you can seriously turn 1/16 to 3/32 consistently then the best on the market is the NSK a 400,000 rpm air drill with a wonderfully easy to use hand piece, there are dental handpieces that run on air that will do the same thing the NSK does yet they are cheaper. Like Ron said treelineusa.com  is a great place to buy the tiny bits like Bhin Pho used. If you can only turn wall thickness to 1/8" + maybe another 1/16 then the micro-motor tools and there are quite a few of them out there, any will work, they run at 45,000 RPMs and the only place I found bits that will pierce this thick are from Packard wood works they are called (2 Piece Mini Saw/Drill Set) these will work in micro motor tools and even a dremel  they are made to drill then cut sideways. I hope this helps some