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Workmanship aside the main quality factor is material. Taps and dies made from high carbon steel are cheaper than ones made from high speed(HS) tool steel. For general use stay away from those made from carbide or exotic alloys. Not only are these very expensive, they are also easier to break than "regular" ones. Adjustable dies are more expensive and more versatile. But along with this comes the ability to accidentally cut the thread too small. Often more handy than round dies are ones with hex or 12 point outside diameters. Unfortunately tool steel dies are very hard to find in anything other round OD. There are however, holders for round dies that allow the use of a wrench or socket, a square drive ratchet or extension, or a chuck. But, these holders may not fit into a space where a hex or 12 point die might. Dies are available in different outside sizes. While the larger ones are a little stiffer, for working on machinery the smallest ones available are going to be the most useful. A packaged set isn't necessarily cheaper than buying the comparable individual items from an industrial tool supplier. Going this route affords the opportunity of having the exact combination of type(pipe, starting, bottoming, spiral point, etc.), manufacturer, sizes, OD, material, die holder, tap handles, and storage box that you want. You might also consider a set of "thread chasers" or "thread restorers". They are not very expensive, and can often clean up rusty or mildly damaged threads with little or no material removal. And, the dies(they look like nuts) will often fit into areas where no standard die would clear. Good luck...Al English
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