The logic of limit gauging is that a manufactured part is acceptable when every feature lies between a maximum and a minimum. Measuring a feature gives a number, which then has to be compared with two limits and is subject to the measurement uncertainty of the instrument. Gauging removes the number: the go gauge embodies the maximum material limit and the no-go gauge embodies the least material limit, so acceptance becomes a pass or fail with no arithmetic.
For a cap thread, maximum material is the condition with the most metal, so the go gauge is the largest thread that must still fit and the no-go gauge is the smallest that must not fit. For a holder, the roles invert because the feature being checked is a bore or a socket. Getting this backwards is the single most common error in a new inspection setup, and it produces a line that passes everything.
Run the go gauge first, without force, using only the weight of the gauge or a defined light push. If it does not enter, stop: the part is rejected regardless of the no-go result. Then apply the no-go gauge, which must not enter more than the stated engagement. Applying force to make a go gauge enter tests the hardness of the gauge, not the part.
Limit gauges check size and form at its own features only. They say nothing about the position of a pin relative to a shell, the squareness of a cap face, or the depth of a contact. Those need their own gauge sheets or a functional check in a reference holder.
