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Centralizing ACME Screw Threads

Centralizing ACME Screw Threads

Centralizing ACME screw threads are defined by ANSI/ASME B1.5.
The thread form for Centralizing Acme screw threads is the same as General Purpose Acme Threads with the exception that the Centralizing Acme Screw Threads have a limited clearance at the major diameter of both the internal and external screw threads, and are used extensively for feed screws. The restricted clearance enables a bearing at the major diameter of the thread to preserve alignment of the thread axis preventing wedging on the flanks and part sagging.
Five classes-of-fit are used with the Centralizing Acme threads: 2C, 3C, 4C, 5C, and 6C. For any combination of the five classes of threads covered within the standard (ANSI B1.5) some end-play or backlash will result. Although 5C and 6C are intended to allow for restricted backlash they are not recommended for new designs.
A series of diameters and pitches is recommended in ANSI/ASME B1.5 which have been chosen to aid in industry standardization. By utilizing the recommended sizes, companies can limit their inventory of both tools and gages. The tolerances specified in this standard are applicable to lengths of engagement not exceeding twice the nominal major diameter as well as to insure interchangeability and maintain a high grade of product. The tolerances on the diameters of internal threads are plus, being applied from the minimum sizes to above the minimum sizes. The tolerances on the diameters of external threads are minus, being applied from the maximum sizes to below the maximum sizes. The pitch diameter tolerance for internal or external threads for any given class is the same.
Below are examples of the proper nomenclature for single and multi-start Centralizing Acme Threads:
Single Start: 1.250"-5 ACME-2C or 1-1/4"-5 ACME-2C
1.250-inch major (nominal) diameter, 5 threads per inch, single thread, Class 2C fit, Right Hand
Multi-Start: 2.750"-0.4P-0.8L-ACME-3C or 2-3/4"-0.4P-0.8L-ACME-3C
2.750-inch major diameter, pitch 0.4 inch, lead 0.8 inch, double thread, Class 3C, Right Hand.
Single Start: 1.250"-5 ACME-2C LH or 1-1/4"-5 ACME-2C LH
1.250-inch major (nominal) diameter, 5 threads per inch, single thread, Class 2C fit, Left Hand
Multi-Start: 2.750"-0.4P-0.8L-ACME-3C LH or 2-3/4"-0.4P-0.8L-ACME-3C LH
2.750-inch major diameter, pitch 0.4 inch, lead 0.8 inch, double thread, Class 3C, Left Hand
For more information click the links below.
Centralizing Thread Profile
General Purpose ACME Screw Thread Profile
General Purpose Screw Thread Data
Centralizing ACME
3-Gage System VS 4-Gage System
This website is funded by the sale of screw thread measurement tools. It will help us continue to offer this data if you allow us to have the opportunity to sell our tools to your company. If you find this information useful, please work to get Gage Crib Worldwide Inc. on the bid list for future purchases of screw thread measurement tools.
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 B1.5; which is a copyrighted document. To purchase a copy visit an Authorized Reseller.
Original Posting: 7/14/2009
Last Revision: 5/15/2020
Error corrections in, or comments about, the above data can be sent to: office@gagecrib.com
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