Fixed Limit Gages...What Are They?

The word gage, when used by itself, is about as general and unspecific in its meaning as the companion word tool. In discussing gages, we must first narrow the field down to a manageable size. First, then, we are talking about production gages, which came into being as a necessary step in the development of assembly-line production. When a manufacturing company undertakes to produce a complex assembly, like a new Wankel engine, it is generally economical to assign production of the numerous parts to subsidiary plants and subcontractors where the specialized machines and skills are available. It follows that large numbers of shafts and bearings, screws and nuts and other assorted parts may be stockpiled at the assembly plant without having been test-fitted. If it is now possible to select parts at random and fit them into a functioning assembly, it is only because gages existed and this manufacturer knew how to use them.

Machine operators, working on parts with critical dimensions, were provided with gages, so that they could keep a check on wearing tools and other machine problems which prevent absolute uniformity in their work. The parts were then carefully spot-checked with gages in the subcontractor's inspection department before being shipped, and again at the assembly plant when received. This defines the area occupied by production gages. They are not often used in a home workshop. But in a complex industrial organization, they are all-important.

In order to limit this discussion to a manageable level, we are going to talk exclusively about fixed-limit gages, which are basic and foolproof in their use. Fixed limit, or Go / NoGo gages are 'Attribute gages'. Attribute gages check the extreme limits of the product tolerance letting you know the product is within its manufacturing limits. This will eliminate the extremely sensitive measuring equipment, which must be used under controlled laboratory conditions. It will also eliminate many devices, which have been designed to check concentricity, squareness, parallelism, exact position and other relationships between features, which are required in assembly. We are now restricted to checking a blueprint dimension given for a single feature - the diameter of a hole, the effective size of a screw thread, thickness, length, and the like.