General Purpose ACME Screw Thread Data per ANSI/ASME B1.5

The General Purpose threads consist of 29° included angle and a series of diameters and related pitches, as recommended in the ANSI B1.5 Standard. These diameters and pitches have been chosen to meet current requirements with the least number of items in order to condense amount of inventory of both tools and gages. The tolerances specified in this standard are relevant to lengths of engagement not greater than twice the nominal major diameter.

Three classes of General Purpose threads, 2G, 3G, and 4G, are provided in the standard, each having clearance on all diameters for free movement, and may be used in assemblies with the internal thread rigidly fixed and movement of the external thread in a direction perpendicular to its axis limited by its bearing or bearings. It is suggested that external and internal threads of the same class be used together for general purpose assemblies, Class 2G being the preferred choice. If less backlash or end play is desired, Classes 3G and 4G are provided. Class 5G is not recommended for new designs.

The tolerances contained by the standard are designed to ensure interchangeability and maintain a high grade of product. The tolerances on diameters of the internal thread are plus, being applied from minimum sizes to above the minimum sizes. The tolerances on diameters of the external thread are minus, being applied from the maximum sizes to below the maximum sizes. The pitch diameter (or thread thickness) tolerances for an external or internal thread of a known class are the same. The thread thickness tolerance is 0.259 times the pitch diameter tolerance.

Below are examples of the proper nomenclature for single and multi-start General purpose ACME Threads:

Single Start: 1.250"-5 ACME-2G or 1-1/4"-5 ACME-2G
1.250-inch major (nominal) diameter, 5 threads per inch, single thread, Class 2G fit, right hand

Multi-Start: 2.750"-0.4P-0.8L-ACME-3G or 2-3/4"-0.4P-0.8L-ACME-3G
2.750-inch major diameter, pitch 0.4 inch, lead 0.8 inch, double thread, Class 3G, right hand.

Single Start: 1.250"-5 ACME-2G LH or 1-1/4"-5 ACME-2G LH
1.250-inch major (nominal) diameter, 5 threads per inch, single thread, Class 2G fit, Left hand

Multi-Start: 2.750"-0.4P-0.8L-ACME-3G LH or 2-3/4"-0.4P-0.8L-ACME-3G LH
2.750-inch major diameter, pitch 0.4 inch, lead 0.8 inch, double thread, Class 3G, Left hand.
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For more information click the links below.
" General Purpose Thread Profile
" General Purpose Thread Data

If you have a pressing need for this information contact Wayne at:gageguy@gagecrib.com