1. What are Limit Gauges ?
Limit gauges are inspection tools used to check whether the dimensions of a component lie within specified limits (tolerances). Instead of giving an exact measurement, they simply indicate whether a part is:
- Acceptable (within limits)
- Rejectable (outside limits)
This concept is based on Taylor’s Principle of Limit Gauging.
Table of Contents
2. Taylor’s Principle of Limit Gauging
According to Taylor:
- GO Gauge
- Should check the maximum material condition (MMC)
- Must pass completely over/through the component
- NO-GO Gauge
- Should check the minimum material condition (LMC)
- Must NOT pass over/through the component
3. Types of Limit Gauges
3.1 Plug Gauges (For Holes)
Description
- Used to check internal dimensions (holes)
Types
- Double-ended plug gauge
- Progressive plug gauge
Working
- GO end should enter the hole
- NO-GO end should not enter
3.2 Snap Gauges (For Shafts)
Description
- Used to check external dimensions (shafts)
Types
- Double-ended snap gauge
- Progressive snap gauge
- Adjustable snap gauge
Working
- GO side should pass over shaft
- NO-GO side should not pass
3.3 Ring Gauges
Description
- Circular gauges used to check shaft diameters
4
Types
- Plain ring gauge
- Thread ring gauge
3.4 Thread Gauges
Description
- Used for checking screw threads
Types
- Thread plug gauge (internal threads)
- Thread ring gauge (external threads)
4
3.5 Feeler Gauges
Description
- Set of thin metal strips used to measure small gaps
4
4. Design Considerations of Limit Gauges
- Wear allowance
- Gauge tolerance
- Material selection (hardened steel)
- Proper marking (GO/NO-GO)
- Size and shape
5. Advantages of Limit Gauges
- Quick inspection
- No need for skilled operator
- Suitable for mass production
- Eliminates measurement errors
- Ensures interchangeability
6. Disadvantages of Limit Gauges
- Do not provide exact size
- Separate gauges required for each dimension
- Wear can affect accuracy
- Initial cost is high
7. Applications of Limit Gauges
- Mass production industries
- Automotive manufacturing
- Machine tool inspection
- Quality control departments
- Assembly line inspection
8. Difference Between Limit Gauges and Measuring Instruments
| Feature | Limit Gauges | Measuring Instruments |
|---|---|---|
| Output | Pass/Fail | Actual value |
| Speed | Very fast | Slower |
| Skill required | Low | Moderate |
| Accuracy | High (within limits) | High (exact measurement) |