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Nymo thread comes in various sizes. Sizes most common for beading are 00 through F. The smallest is 00, then comes A/0, then B,D,and F. Sizes larger than that would be for sewing heavy leather and for bead stringing.
Silamide thread is pre-waxed and is available in Size A.
Miyuki beading thread is twisted nylon and is available in Size B.