The rotary grinding and polishing tool or the 8-bit mini rotary tool set with diamond coated steel bits will handle metals. These tools hold a variety of drill bit sizes. Accessory kits are available for these tools. Caution and safety considerations, such as safety glasses, should be taken with the speed which you use these motorized tools.
To prepare the metal for drilling, you should mark the spot with an ink marker, and dimple the mark on the metal with a center punch (or household steel nail) and hammer. Hold the metal piece stationary in a vise or steady on a block of wood with a hand held gripping tool, such as a ring clamp. Place the drill bit at the mark and it will find its way to the dimple on contact and not skip along the surface of the metal. Drill at a slow speed so that the metal does not get too hot and expand.
There are also hole-punch tools available for punching through metal. These require that you mark your spot and center the cutting punch. It is an accurate and easy finishing approach.
When creating holes with any method, burs or splinters of metal may form at the top and bottom surface from the pressure of drilling. Finishing, that is, cleaning up the hole, is important, especially if you plan to insert thread, coated stringing wire or even metal wires through the hole(s). Reamers, sanding and buffing accessories for the rotary tools are a perfect way to clean up those metal splinters.
Drilling into gemstones, specifically your howlite pendant, requires different techniques and drill bits and burs when drilling metal. Manual reamers and beading awls are available with diamond-coated bits in various sizes that will widen and clean out existing holes in stone.
For automatic stone drilling, you should use the rotary tools listed above with diamond-coated drill bits and burs. Be aware that stones are porous and may break when holes are widened or new holes are started with too much force. You can create a dimple using a diamond coated bur, similar to dimpling metal with a center punch. Using a coolant (such as water) is also recommended as it helps reduce heat and friction from the automatic drilling of stone, as well as reduces the dust. This is particularly relevant to pearl drilling. You may also wish to use a ring clamp or other buffered gripping tool for stability while you drill the stone pendant.
It is best to gain an understanding of stone porosity and if there are any hazards to be considered with stone dust when altering stone pieces, such as making a new hole.