number and letter drills come in sizes that are only a thousandth or a few ten-thousandths of an inch increase in diameter. between number bits and letter bits it is possible to have a range of drilled holes for just about any given diameter pin you might have. you have to first drill a "try hole" in a piece of scrap, to get the diameter of the hole that is smaller than what you want and then use bits that give you the exact size you're looking for. no drill bit drills exactly the size hole stated on the bit,....usually, they all drill holes slightly larger than the size stated. reamers will work as g-rock says, so will my method...... you are essentially using the number and letter bits as reamers. they can be spun with a pin vise with your fingers once the first hole is drilled. number and letter bits are much easier to come by than precision number and letter size reamers and the reamers are allot more expensive. with a reamer you are not guaranteed the size hole stated on the reamer either,( if you spin the reamer by hand, wobble will increase the size hole they make, at that point you are at the same point as using drill bits,......so why spend the money for reamers .... there is just as much possibility that you might need to buy another reamer or two, to get that precise fit.
we can go on and on about which method works better,....they both work,.... I know my method works fine, with potentially less expense.