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Pitch Diameter Changes for 1A and 1B

ANSI/ASME B1.1:2003 Pitch Diameter Changes for 1A and 1B

In 2003 the ASME B1 Committee finalized changes to ANSI B1.1. This page only talks about pitch diameter changes. Many of the tabulated screw thread pitch diameter sizes remained the same. The tabulated screw thread pitch diameters which changed only moved 0.0001 to 0.0002 of an inch. This small amount of change is considered insignificant to fit and function of the threaded assembly, but important enough to change to help assure consistency in the future.

There were no changes for:
Internal 1B minimum pitch diameter
External 1B maximum pitch diameter
Internal 2B minimum pitch diameter
External 3A maximum pitch diameter
Internal 3B minimum pitch diameter

Changes to 1A and 1B:
The data which remained unchanged is not contained in this chart.

Screw Thread Size
7/16"-20 UNF
5/8"-11 UNC

Other Changes:
This page only speaks to ANSI/ASME B1.1:2003 pitch diameter changes because the screw thread pitch diameter is a very visible screw thread size component. Other features of the screw thread did also change, again to an insignificant degree. The complete list of changes are outlined in the appendix to ANSI/ASME B1.1:2003.

The Goal:
The The intent of the authors of the standard is that the world move to the newest version of the standard with all possible haste. It is understood that disputes will arise over minutia, but the authors seem to indicate that the minutia is insignificant to the fit and function of the end product. The parties involved in any dispute related to these changes to this standard should resolve it with an eye toward fit and function in existing parts; flexibility of designs to absorb changes in the standard; and minimal cost consequences for all parties involved. It is known that many prints contain pitch diameter or other data related to thread information, which was in agreement with the older version of the standard, but now is in conflict with the new version of the standard. That old data should be revised, or deviated to meet the new standard requirements in all cases.

Related Pages
ANSI/ASME B1.1:2003 Changes
Pitch Diameter Changes for 1A and 1B
Pitch Diameter Changes for 2A and 2B
Pitch Diameter Changes for 3A and 3B


This data is provided for general information only. The intention is to provide accurate information; regardless; errors may exist in the supplied information. If accuracy is critical, base your final decisions on the data provided in the root document: ANSI/ASME B1.1:2003. ANSI/ASME B1.1:2003 is a copyrighted document. To purchase a copy visit an Authorized Reseller.

Original Posting: 6/15/2010
Last Revision:
Error corrections in, or comments about, the above data can be sent to: office@gagecrib.com

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