Drill sizes are a bit illogical, it seems. The usual 'set to have' is the number drills, from 1 to 80. Some of the drill diameters are only 1 or two thousandths of an inch apart from one number to the next, while others are 5 or more thou apart. The next most common set is fractional inches, and there is also a letter set, from A to Z, which supplies some sizes that are in between the sizes in the other sets. There are also 'spade drills' which can be a savior, since you can make them yourself. A spade drill is simply a piece of drill rod with one end hammered flat and filed so that it will cut. For drilling plastics, that's all you need to do. However a useful skill in making drills is 'case hardening' - you use a piece of mild steel ('cold rolled') rod or wire to make the spade drill bit, then cook the tip, red hot, in case hardening compound (or most any form of carbon) for a few minutes and quench it. This leaves a glass-hard surface and there is no need to temper it like all tool steel drills ('temper' is 'soften') so they last a goodish while.
So the short answer has been given in a previous reply, but if you're working with plastics in small scales you can get away with a lot when making your own.
Google 'spade drill' and 'case hardening compound for more info.
Lots of possibilities for the adventurous, in any scale up to 12 inches to the foot (and beyond).
- Bill