A gauge drawing is short, and almost all of its useful content is in three places: the dimensioned view, the tolerance table, and the note that says whether the gauge is a go or a no-go member. Reading it in that order prevents the most common mistake, which is to treat the gauge as a master part and measure the cap against it with a caliper.
Each dimensioned feature on a gauge carries its own manufacturing tolerance, usually a few micrometres for a hardened steel gauge. The nominal value already includes a wear allowance in some designs and not in others, and the sheet states which. A gauge made to the nominal without the stated tolerance is not a compliant gauge even if it looks right.
A go gauge is made to the maximum material condition of the feature it checks, so it must enter or mate. A no-go gauge is made to the least material condition, so it must not enter. They are often supplied as a pair on the same holder or as two separate items with different sheet numbers, and swapping them silently reverses every result on the line.
Gauge sheets get revised, and the revision letter or number is printed with the sheet reference. A 7006-xx sheet with a later amendment can change a dimension by a few hundredths of a millimetre. If the gauge in the inspection room was bought against an older amendment than the one in the purchase contract, the two documents disagree and neither party will notice until a lot is rejected at the border.
