1. Gauging Devices

2. What are they used for
We use gauging devices to determine if a component is within the specified limits of size when there are large numbers of items to be checked as it is much quicker than measuring each item with an instrument. Gauging devices do not give a direct reading; they only determine if a component is within the lower and upper limit of size by comparison with the particular size and type of gauge, they are a form of comparator. The go end/part of a gauge depending on type should fit over or inside the component and the no-go end/part should not fit over or inside component.

3. Plug Gauge
Plug gauges are used to measure holes/bores to determine if they are within the specified tolerance (limits of size). They are ground so one end is slightly larger than the upper limit of the bore so it should not fit (No Go) the other end is ground slightly larger than the lower limit of the bore so it should fit into the hole/bore. Each end is offered up to the bore, if the bore is correct then the Go end will slide into the bore and the No Go end will not slide in, if both ends slide in then the bore is too large, if neither end slides in then the bore is too small.

4. Ring Gauge
Ring gauges are used to measure shafts to determine if they are within the specified limits of size
The bore of the Go gauge is machined so it is fractionally larger than the upper limit of size of the shaft and the bore of the No Go gauge is machined so it is fractionally smaller than the lower limit of size of the shaft.
To use the ring gauges you offer them up to the shaft and try to slide them over the diameter.
If the Go gauge slides over the shaft but the No Go does not the shaft is within tolerance
If both gauges fit over the diameter the shaft is to small
If the go gauge does not fit over the diameter the shaft is to large

5. Adjustable Calliper (Snap) Gauges
Adjustable Calliper (also known as Adjustable Snap Gauges) are used to measure external measurements to determine if they are within the specified limits of size, they operate on a similar principle to ring gauges but are designed in such a way that they slide over the diameter/thickness of the material as opposed to the material sliding inside the bore. The Go part of the calliper is adjusted so it is fractionally larger than the upper limit of size of the component and the No Go part adjusted so it is fractionally smaller than the lower limit of size of the shaft. To use the calliper gauge you slide it over the diameter, the Go end should slide over the component but the No Go end should not slide over the component.

6. Screw plug gauge
A screw plug gauge is similar to a plug gauge but instead of having flat parallel faces, it has a screw profile matching that of the thread type/pitch to be measured. It is used in a similar way as the plug gauge but is screwed in rather than pushed in, the Go end screwing right in and the No Go end unable to screw in.
They can be double ended, progressive or single ended

7. Adjustable Calliper Screw Gauge
Adjustable calliper screw gauges are similar to standard calliper gauges except instead of having flat faces/anvils it has a screw thread profile to match the pitch/type of thread being measure, the operation is exactly the same as that of the standard calliper gauge, see diagram opposite

8. Tapered Plug Gauge
A tapered plug gauge is ground to the correct angle and has a step machined at the larger diameter just below the end of the taper a specified distance down depending on specification, this step will determine if the taper is the correct size. When placed in the tapered bore the step should be below the end of the bore but the end of the tapered plug should not go into the bore as in diagram opposite. If the step does not go into the bore then it is to small, if the end of the taper enters the bore then it is too large, see diagram opposite

9. Tapered Ring Gauge
A tapered ring gauge is internally ground to the correct angle and like the plug gauge, there is a step machined on the top. The principle of operation is similar to that of the plug gauge but in this case, you place the ring over the tapered shaft and the position of the step indicates if it is within the specified limits. If the shaft is correct the ring will not go completely over the shaft, but will go on beyond the step, if the ring goes over the shaft completely then the shaft is too small, if the shaft does not reach the step then it is too large as in drawing

10. Swing Gauge
Swing gauges are used to check the depth of a cut-out/recess in a component, one end is machined fractionally longer than the minimum depth, and the other end is machined to fractionally shorter than the maximum depth. When the Go end of the gauge is placed in the recess it should be free to swing, if it touches the bottom then the recess is to shallow. When the No Go end is placed in the recess it should touch the bottom, if it is free to swing then the recess is too deep.

11. Thumb Nail Gauge
The Thumb Nail Gauge is another method of gauging the depth of a recess
It consists of two parts, a ring which sits on top of the component and a shaft that slides inside the ring and into the recess as shown.
The shaft is the length of the ring plus the minimum depth of the recess plus the tolerance, it has a step machined on the top which is equal to the tolerance and is used as shown in the diagram far right.

12. Step Gauge
Step Gauges are used to measure the length of steps on shafts or other components to ensure they are within the specified tolerance.
As shown in the diagram the step on the gauge is equal to the tolerance on the height or length from the shoulder
For Example if the step was 20mm +/ then the first step would be 19.85mm from the base and the second step would be mm from base.
The diagram on the far side shows how it is used.