Where in the world did you learn that B16.5 does not cover sizes below 2 inch? In fact, the 2013 version covers sizes of NPS 1/2, 3/4, 1, 1 1/4, 1 1/2, 2, 2 1/2, 3, 3 1/2, 4, 5, 6, 8, 10, 12, 14, 16, 18, 20, and 24.
The previous thread you linked deals with a completely separate issue, which is that in certain sizes, flange dimensions for some pressure classes are identical to other pressure classes:
- 400 Class flanges are dimensionally the same as 600 Class flanges in sizes NPS 1/2, 3/4, 1, 1 1/4, 1 1/2, 2, 2 1/2, 3, and 3 1/2 (so when you look up dimensions for these 400 Class flanges, the table directs you to use dimensions for 600 Class flanges).
- 900 Class flanges are dimensionally the same as 1500 Class flanges in sizes NPS 1/2, 3/4, 1, 1 1/4, 1 1/2, 2, and 2 1/2.
That previous thread specifically dealt with NPS 2 900/1500 Class flanges, but there is nothing that says B16.5 doesn't cover flanges smaller than NPS 2.
What are you doing that you "want" something like 1/4" or 3/8" flanges?
At some point, and 1/2" sounds like it's that point, the size of the flange and necessary bolts for really small piping just doesn't make sense. Can you just use 1/2" piping if you are determined to use flanges?
I would think that needing flanges smaller than NPS 1/2 is getting into the instrumentation realm, and I'm afraid I'm not much help there. It's typical to use threaded fittings of various types for such small sizes, but I also know there are some industries where threaded fittings are frowned upon. Perhaps check out some subsea specs.
Since ASME B16 starts from NPS 1/2", what you can do is trying to assemble your valve with a set of instrumentation fittings and a flange adapter-to-fitting. There are good options, like Swagelok, which has a lot of options in this way. If this idea can be acceptable, so you can range from 1/16" to 2".