Greenfield, Widia and Brubaker are good names. Buy as you need is a good way, I have not found a good set of taps in a kit. Most kits do not cover gun smithing sizes any ways. Most off the shelf kits have lousy taps that don't cut metal well and usually out of spec. I keep on hand at least 6-40 and 8-36, for most rifle applications. These taps can be bought from Mcmaster-Carr, mcmaster.com and MSC, mscdirect.com. Try not to use TiN coated taps on aluminum, even with lube the aluminum can stick to the TiN coating and cause problems. There are several types of taps as well. Spiral point aka "gun" taps that push the chip in front of the tap, for thru holes, spiral flute "machine taps" that pull the chip out of the hole, "taper" for starting the threads, "plug" for continuing the threads and "bottom" for tapping blind holes very close to the bottom. The only difference on the last 3 are the number or threads in the lead-in, how tapered the tip is. Each tap size will need a specific drill size as well. Have fun and good luck.