Aside from higher number = smaller size needle, it seems somewhat arbitrary to me? I'm guessing it's to distinguish tapestry (blunt) needles from other common (sharp) types. The other common types use a numbering system between #1 to #12 (with a few exceptions). Tapestry needles start at #13.
(E.g., #26 tapestry and #8 embroidery needles are the same diameter (0.61 mm) and length (34 mm). #24 tapestry is the same diameter (0.76 mm) as #5 embroidery, but is shorter (37 mm vs 41.5 mm).)
The John James website has a neat needle size guide for comparison.
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branchandroot
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Date: 2020-07-21 09:01 pm (UTC)(E.g., #26 tapestry and #8 embroidery needles are the same diameter (0.61 mm) and length (34 mm). #24 tapestry is the same diameter (0.76 mm) as #5 embroidery, but is shorter (37 mm vs 41.5 mm).)
The John James website has a neat needle size guide for comparison.