Years ago I bought one of the ~$10 hard case assortments (Harbor Freight, et. al.) and it has more than paid for itself despite having only a few useful sizes. I got the inch assortment…dash, AS568, whatever you want to call it. If metric sizes would be more useful to you, read the label carefully. Many of the metric kits contain dash sizes and all they’ve done is converted the measurements to mm and printed a new label.
Nevertheless even the “wrong” assortment can get you out of a bind. Many times a dash size can be used to replace a metric, or vice-versa. And here’s a little trick that works well when you have an O-ring that’s just barely too thick. Slip it over a mandrel (shank of a drill bit or a transfer punch) and spin it in the drill press. Then take a Dremel loaded with a rubberized polishing wheel and gently kiss the OD of the O-ring as it spins. Abrade it down slightly for a proper fit. I can’t tell you how many times this has made the difference between waiting days for a replacement versus being up and running again in 10 minutes.
Like others have said, you will inevitably need other sizes and perhaps different materials or durometers for some applications. There are far too many possibilities for any assortment to be a catch-all so plan to order some sizes as you need them.
