In the high-precision world of industrial manufacturing, machinists implement a broad range of measuring tools. One of the most vast and versatile is the handheld gage. Handheld gages range from the familiar digital micrometer to tools as basic as a ruler, and everything in between. A member of the handheld family, the ring gage is a cylindrical measuring device with a precision lapped, nearly perfect geometry and a precisely determined internal diameter. Ring gages have two primary functions in manufacturing: a point of reference for setting other measuring instruments, or indirect gaging, and checking the size and roundness of manufactured parts, or direct gaging.

Indirect gaging

The process of indirect gaging with a ring gage involves using the tool in conjunction with another precision measuring device. In this application, the gage is frequently used with measuring tools such as bore gages and air gages. In this setup, the manufacturer uses a master ring gage. A master ring is a gage that has been manufactured with a bilateral tolerance. By definition, a bilateral tolerance applies to one half of the specified tolerance plus and minus from the designated size usually deviating not more than 0.00001 inch from the ring gage's nominal size (Class XX).

The use of a ring gage establishes a point of reference for a comparative measurement process in which the size of the manufactured work piece is directly compared to the known and certified value of the ring. Because of the light wear produced by indirect gaging, ring gages should be recalibrated approximately once per year to ensure the continued integrity of the gage and its measuring accuracy.

Direct gaging

Ring gages used for direct gaging, or fixed-limit gaging, aid the manufacturer in establishing a physical limit for the maximum acceptable outer diameter of a work piece. In addition, ring gages help determine a lack of roundness in the part that may not be picked up by a micrometer or other commonly used comparators. In this instance, the part may measure correctly in size with a micrometer but will not fit through the ring gage. Detecting such defects will ensure that all manufactured parts fit correctly in high-precision tool holders and bearing races used by manufacturers.

A ring gage used in this manner is called a go gage. It is manufactured to the high limit of the part tolerance and has a unilateral minus tolerance. However, sometimes in the manufacturing process, it is necessary to evaluate the low end of part tolerance, so a no go gage would be implemented. A no go gage is produced to the low limit of the part tolerance and has a unilateral plus tolerance.

When working with a go gage, a correctly sized work piece will pass completely through the gage, whereas an oversize part will not pass through the gage. Conversely, if a part passes through the no go gage, it is considered undersized and is unacceptable. Because direct gages tend to have frequent contact with work pieces and are exposed to the everyday shop environment, it is important that they maintain a higher recalibration recall than gage masters.

Consistent use of go, no go and master ring gages provides manufacturers with an indisputable method of determining part consistency and quality.

Additional information may be attainted through the standard, ANSI/ASME B89.1.6M.