Gage Blocks Information
Gage blocks are manufactured to precise gage-maker tolerance grades for calibrating, checking, and setting fixed and comparative gages. Rectangular, square, wear, scribing, and angle gage blocks are available in hardened steel, carbide, and ceramic materials. Tolerance grades range from Lab Master or Grade 0.5 (AAA) blocks with +/- 1 micro-inches tolerances for standards laboratories to the lower inspection or working Grade 3 (A) blocks for gaging, setting, and general inspection operations in production or tool room areas. Other proprietary blocks may be available for specific applications with higher or lower tolerances and configurations.
Types of gage blocks include:
Angular gage blocks are manufactured to a precise angle for gaging angles or for checking angle gages and protractors. Square gage blocks do not have a central hole and are held together with an external gage block holder. Rectangular gage blocks have one or more centrally located holes for mounting on holding bars. Wear gage blocks are used on the ends of the gage block stack that contact the parts or variable gages being evaluated. Gage blocks can come in a set of several gages and accessories packaged into a kit usually in a case with adjusting tools. Tool kits sometimes contain alternate extensions and contact tips, holders, bases, or standards. Measurement units for gage blocks can be either English or metric. Some are configured to measure both.
Important specifications to consider for gage blocks include:
- block size
- set range
- set steps or increments
- tolerance grade
Gage block size is the thickness, diameter, length, or other dimension of the dimensional standard. Set range is the total length or dimensional range that the set of gage blocks can measure. Set steps are the dimensional size increments or steps in a set of gage blocks or other dimensional standards.
Tolerance grade can be Grade 0.5 (Lab Master or AAA), 1 (AA), 2 (A1/A+), or 3 (A). Federal Grade 0.5, Grade AAA, or Laboratory Master Grade products provide the highest degree of accuracy and are used in precision or master calibration gaging operations in temperature controlled metrology or standards laboratories. Grade 0.5 gage blocks under one inch in length should have length tolerances of +/- 1 micro-inches (1 mike or 1 millionth of an inch) and flatness and parallelism variation of not more than 1 micro-inch. Federal Grade 0.5 exceeds German Grade 00 as well as DIN, ISO, and BSS Grade K.
Federal Grade 1, Grade AA, or Laboratory Grade products provide a high degree of accuracy and are used in precision gage checking or setting operations in quality control or metrology laboratories. Grade 1 gage blocks under one inch in length should have length tolerances of +/- 2 micro-inches (2 mikes or 2 millionths of an inch) and flatness and parallelism variation of not more than 2 micro-inches. Federal Grade 1 exceeds German Grade 00 as well as DIN, ISO, and BSS Grade K.
Federal Grade 2 or Grade A or Inspection Grade products provide a high degree of accuracy and are used in precision gage checking or setting operations in quality control or metrology laboratories. Grade A+ block indicates a manufacturer that provides a higher level of precision compared to the government Grade A standards. Grade gage blocks under one inch in length should have length tolerances of +/- 2 micro-inches (2 mikes or 2 millionths of an inch) and flatness and parallelism variation of not more than 2 micro-inches. Federal Grade 2 exceeds German, DIN, ISO, and BSS Grade 0 standards.
Grade A, or Inspection Grade, products provide sufficient accuracy for use in gaging, setting, and general inspection operations in production or tool room areas.
Features common to gage blocks include marking capability and NIST traceability. Gages that accommodate a scribe or other device for accurately marking a component at a specific measurement along a particular dimension have marking capability. A gage that is an NIST traceable gage has been compared to a master standard that has been checked against an NIST standard.
Glenn McKechnie / CC BY-SA 3.0