Nut: hex

JIS B 1181 Small Hex

JIS B 1181 Small Hex - Small hexagon nuts (Annex JA), types 1, 2 and 3

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Small hexagon nuts of JIS B 1181:2014, Annex JA, the Japanese nuts that do not follow ISO: narrower across flats and lower than ISO 4032 nuts of the same thread. The small series is narrower across flats than the regular nuts of the same thread: 12 mm for M8, 14 mm for M10 and 17 mm for M12, where ISO 4032 has 13, 16 and 18 mm. The heights are those of the regular annex nuts and lower than ISO 4032: about 0.8d for types 1 and 2 and about 0.6d for the thin type 3. Type 1 is chamfered at 30 degrees on the top face only and bears on its flat face, and types 2 and 3 are chamfered on both faces. The width across corners is the theoretical value the standard gives. Both finish grades share these nominal dimensions; thread tolerance is 6H unless specified, and steel nuts of types 1 and 2 are made in strength classes 4T to 8T. The annex reflects production and use in Japan, but it is to be withdrawn and new designs should use ISO-type nuts. Covers M8 to M39 with metric coarse and fine pitch threads; M14, M18, M22, M27, M33 and M39 are second choice.