Go / no-go gauge sizes
Go and no-go gauge sizes for a hole or shaft from the feature limits, with the gaugemaker's tolerance applied inward so a good part never fails on the gauge.
Go / no-go gauge sizes
Size a plug, ring or snap gauge from the part limits. Gauge tolerance goes inside the part tolerance so the gauge can never accept a bad part, only reject a few borderline good ones.
Order it as: GO plug 0.50000 +0.00020 / −0.00000, NO-GO plug 0.50200 +0.00000 / −0.00020 (in).
Product tolerance T = max − min. Gauge tolerance g = T × 10% is the common rule (ASME B89.1.5 and the old 10% rule). Use 5% when the product tolerance is tight or the gauge is a reference master.
Hole, plug gauge: GO = min hole, +g/−0 and NO-GO = max hole, +0/−g.
Shaft, ring or snap gauge: GO = max shaft, +0/−g and NO-GO = min shaft, +g/−0.
Wear allowance moves the GO member further into the part tolerance (bigger plug, smaller ring) so it has life before it wears out of limit. 5% of T is typical where the gauge sees volume.
Gauge classes (ZZ, Z, X, XX) in ASME B89.1.5 set the gaugemaker's tolerance by size range. The percentage here is the sizing rule most shops use when they order. Give the gauge maker the part limits and let them pick the class if you are unsure.
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