Significant changes have been made by NIST for the designation of Class F weights.

As of January 1st, 2020, NIST no longer recommends the purchase of new Class F field weights.

If you manage a calibration service department and have Class F weights in service, these changes may affect your weighing processes currently or in the future.

Read below to learn about changes to NIST Handbook 105-1 and what that means for your Class F field weights.

To read the full NIST Handbook 105 Series, Section 105-1 click here.

Background
Improvements in technology have led to more Class I & II scales being used in commercial applications. With high precision scales being more commonplace, NIST found that many of these devices were being calibrated using low precision Field Weights. Due to this, NIST determined the need for a more detailed categorization of "Field Weights" in order to effectively categorize the discrepancy between precision balances and weights.

Status of Class F Weight
As of Janurary 1st, 2020, NIST HB 105-1 states that no new NIST Class F weights should be placed in service for use of testing commercial weighing equipment. Existing NIST Class F weights can still be used, provided they demonstrate mass stability. However, their usage should be limited to weighing systems with accuracy classes of III, IIIL, and IIII. NIST does not recommend Class F weights be reclassified to an ASTM or OIML classification.

What Weights Should I Use Now?
For the purchase of new field weights, NIST now recommends the following:
  • ASTM E617, Standard Specification for Laboratory Weights and Precision Mass Standards
  • OIML R111-1, International Recommendation, Weights of Classes: E1, E2, F1, F2, M1, M1-2, M2, M2-3 and M3

See the chart below to see which of the ASTM and OIML weight classes meet the needs of your weighting device. You should always consult NIST Handbook 44 to verify the proper mass standard for your scale or balance.

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