1. Introduction to Gage Blocks

Gage blocks (also called slip gauges or Johansson blocks) are precision ground and lapped blocks used as reference standards for linear dimension. Their primary role is to provide traceability for micrometers, calipers, height gauges, and coordinate measuring machines (CMMs). The high degree of flatness, parallelism, and surface finish enables them to be wrung together to build up custom lengths. 

According to ISO 3650 and NIST guidelines, maintaining the integrity of gage blocks requires a robust handling and maintenance program, particularly in calibration and inspection laboratories. 

2. Cleanliness and Handling

Contaminants such as dust, oils, and abrasives can impair surface wringing, increase wear, or introduce measurement errors. 

Cleaning Procedures 

• Clean blocks before and after use with a lint-free cloth and approved solvents (e.g., isopropyl alcohol). 
• Avoid paper towels, which may leave fibers or abrasive particles. 
• Use a light application of rust inhibitor or mineral oil on steel blocks if extended exposure is expected. 

Handling Protocols 

• Always handle blocks by their edges to minimize contamination from fingerprints. 
• Wear powder-free nitrile gloves in high-accuracy applications or in cleanroom environments. 
• Avoid touching measuring surfaces directly. 

Reference: Gage Block Handbook, Chapter 4 — Proper cleaning improves wringability and reduces surface damage . 

3. Wringing Techniques

Wringing is the process of joining gage blocks together using molecular adhesion, without external force or adhesive. 

Best Practices for Wringing: 

• Align the blocks perpendicularly, slide them into contact with moderate pressure and slight rotation. 
• Do not force blocks together, as excessive pressure can cause micro-abrasion. 
• Wring only blocks of the same material unless guided by specific calibration instructions. 

Improper wringing may cause galling or distort the surface finish, directly affecting dimensional integrity . 

4. Environmental Control

Gage blocks are sensitive to environmental influences, especially temperature and humidity. 

Temperature 

• Calibrations should occur at 20.0 ± 0.5°C, as specified in ISO 1. 
• Allow gage blocks to stabilize thermally in the lab environment for several hours prior to use. 

Humidity 

• Maintain relative humidity between 40–60% to minimize corrosion and reduce water film thickness that could affect wringing and measurements. 

According to NIST, water films on block surfaces are typically several nanometers thick at standard humidity, which can affect apparent length during comparison measurements . 

5. Storage and Protection

Proper storage reduces the risk of corrosion, warping, or physical damage. 

• Store gage blocks in a temperature-stable, dry environment. 
• Use foam-lined cases with individual compartments to prevent contact and scratching. 
• Apply rust inhibitors for steel blocks if blocks are to be stored for extended periods. 
• Avoid magnetic fields or strong mechanical vibrations near the storage area. 

Blocks that are wrung together for long periods may suffer permanent adhesion or deformation and should be separated and cleaned after each use. 

6. Inspection and Maintenance

Regular inspection is essential to detect wear, damage, or changes in length over time. 

Visual and Functional Inspection 

• Check for nicks, scratches, or loss of wringability before each use. 
• Suspect blocks should be removed from service and referred for calibration. 

Periodic Calibration 

• Follow calibration intervals based on usage frequency, criticality, and history of drift. 
• Refer to ISO/IEC 17025 and ILAC-G24 for recalibration interval justification. 

According to the Gage Block Handbook, even high-grade blocks can lose dimensional accuracy due to repeated use or corrosion, making inspection and calibration critical for reliable use . 

7. Summary of Best Practices

8. References

• NIST Monograph 180, The Gage Block Handbook, Theodore Doiron and John Beers, 1990 
• ISO 3650:1998, Geometrical Product Specifications (GPS) – Length standards – Gage blocks 
• ISO/IEC 17025:2017, General requirements for the competence of testing and calibration laboratories 
• ILAC-G24:2022, Guidelines for the Determination of Calibration Intervals of Measuring Instruments 

About Richard J. Bagan, Inc. 

Richard J. Bagan, Inc. is an ISO/IEC 17025–accredited calibration laboratory specializing in dimensional, force, torque, and materials testing instrumentation. Our metrology services support manufacturers, laboratories, and regulated industries across the United States. 

For gage block calibration, uncertainty evaluation, or consultation on dimensional standards management, contact our laboratory team.