HHG R 級之精度依據ANSI TAP GH 級公差12.7μm(0.005”) 以階段式設定，每一階 段增加12.7μm 小數第1 位4 捨5 入。
HHG R grade system is made by using the datum 12.7μm(0.005inch) in a step form in accordance with ANSI standard, the limits are established by increments of 12.7μm, the upper limit of R grade is decided by rounding off the grade, No x 12.7μm to 1 decimal.

1.上容許度：12.7 μm × N	Upper limit：12.7 μm × N
2.下容許度：上容許度-12.7 μm	Lower limit：12.7 μm × N-12.7 μm
(N=R 級號)	(N=R Number)

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