Metrology Instruments

Plain Limit Gauges

BS 969 : 1982

This standard specifies the tolerances and limits for simple forms of limit gauges, such as cylindrical plain plug, ring and gap gauges and is intended for reference by component producers and gauge makers when gauge limits have not been stipulated. It specifies gauge tolerances for work piece tolerances in ranges between 0.009mm and 3.200mm and how gauge limits are related to the work piece limits. It also specifies types of gauge according to size and minimum work piece tolerance, dimensions are expressed in millimetres but appropriate values in imperial units are given in appendix C. It may be uneconomical for any company or institution to invest in equipment to the level required in order to calibrate all types of plain limit gauges, particularly those with a small work piece tolerance and therefore small gauge tolerances.

It is highly recommended that an appropriate authority such as a UKAS approved laboratory carries out a full calibration on plain limit gauges at least once a year. In between UKAS calibrations at a frequency based on usage, plain limit gauges should be calibrated in-house. A typical in-house calibration would include a written procedure and an associated calibration record sheet, which would contain as a minimum, the following listed information:

(a) Serial number

(b) Location

(c) Procedure number

(d) Workpiece tolerance

(e) Gauge tolerance

(f) Results

(g) Measurement uncertainty

(h) Sentence if appropriate

(i) Date and calibrators signature

(j) Traceability to National Standards

It is necessary that any person carrying out such calibration work should have received appropriate training and have shown the ability to be confident via a suitable training authority. Training records should be held and maintained.

Following are layouts for typical in-house calibrations for plain limit gauges:

Calibration to be carried out in accordance with in-house procedure number .......................

Serial Number: Make:

Calibration Date: Sizes:

FEATURE EXAMINED                      SPEC.                      MEASURED RESULTS

GO:

NOT GO:

The plain limit gap gauges were visually inspected for damage and the following faults were noted:

MEASUREMENT UNCERTAINTY +/- 0.00

Calibrators Signature: ........................................

A traceability statement in this section would be required for all items and their relevant certification utilised for the calibration of plain limit gap gauges.

Plain Plug Gauges

BS 969 : 1982

Calibration to be carried out in accordance with in-house procedure number .......................

Serial Number: Make:

Calibration Date: Sizes:

FEATURE EXAMINED                  SPEC.                  MEASURED RESULT

                                                                                 FRONT     MIDDLE         BACK

GO:

@ 90 degrees:

NOT GO:

@ 90 degrees:

The plain limit plug gauges were visually inspected for damage and the following faults were noted:

MEASUREMENT UNCERTAINTY +/- 0.00

Calibrators Signature: ........................................

A traceability statement in this section would be required for all items and their relevant certification utilised for the calibration of plain limit plug gauges.