Understanding Go and No-Go Plug Gages: The Importance of the 10% Rule

Precision is crucial in manufacturing and engineering. One vital tool in achieving that precision is the plug gage. Understanding go and no-go plug gages — especially the 10% Rule — is essential for maintaining product quality and performance.

This post explains how these gages work and why the 10% Rule plays an important role in meeting tolerances.

The Role of Go and No-Go Plug Gages

A go plug gage represents the smallest acceptable diameter within a hole’s tolerance range. When the go gage fits into the hole, it confirms the hole is not undersized.

For example, if a hole specification is 10.000 ±0.010 millimeters, the go gage (10.000 mm) should fit smoothly. If it does not, the hole is too small, which can cause assemblies to fail or parts to seize during operation.

A no-go plug gage, on the other hand, represents the largest acceptable diameter. If this gage enters the hole, the hole is too large and exceeds the upper tolerance limit. For example, a no-go gage sized at

should not fit into a hole with a 10.000 ±0.010 mm specification. Oversized holes can lead to loose fits, vibration and compromised assembly integrity.

Understanding the 10% Rule

The 10% Rule is a widely accepted guideline in dimensional inspection and gage design. It states that the tolerance allowed when manufacturing or calibrating a gage should not exceed 10% of the part’s tolerance.

For example, if a hole has a total tolerance of 0.010 mm, each gage — go and no-go — should be made within ±0.001 mm of its nominal size. This ensures the gage is more precise than the part it measures, minimizing inspection error and maintaining confidence in the results.

Applying the 10% Rule helps maintain consistency between the measurement system and the parts being produced. It reduces scrap, rework and assembly issues while improving quality and efficiency.

Why It Matters

Following the 10% Rule ensures that:

• Gages provide accurate pass/fail results.

• Inspection errors are minimized.

• Product dimensions stay within functional limits.

  
  

Companies that adhere to strict tolerance and gaging standards often see measurable improvements, including up to 30% higher production efficiency due to fewer rejections and tighter process control.

Final Thoughts

Maintaining precision in manufacturing depends on proper use and control of go and no-go plug gages. The 10% Rule ensures gages are built and maintained to a level of accuracy suitable for the tolerances they inspect.

By following these principles, manufacturers can achieve reliable fits, reduce waste and ensure every part meets its design specifications. In precision engineering, small tolerances make a big difference — and the 10% Rule helps keep that difference under control.