Ring & Plug Thread Gages  
 
Call 616 954 6581 for Thread Gages
About Ring & Plug Thread GagesUsed - Surplus Ring & Plug Thread GagesRing & Plug Thread Gage Technical InformationRing & Plug Thread Gage CatalogsContact Ring & Plug Thread GagesBookmark

 

 
 
 
 
 
Screw Thread Designations per ANSI/ASME B1.1

UN = Unified National Fixed Pitch Series
UNC = Unified National Coarse Series
UNF = Unified National Fine Series
UNEF = Unified National Extra Fine Series
UNS = Unified National Special

Screw Thread Designation Rules

These designations are defined in ANSI/ASME B1.1 with modifications defined in ANSI/ASME SAE AS8879. For full details I suggest reading the standards; however; here is a summation of the designation system defined in these standards:

The first designation is simply: UN. UN = Unified National. UN is used for a set of specific thread series which have uniform or constant threads-per-inch. The eight constant threads-per-inch (TPI) series are: 4-TPI; 6-TPI; 8-TPI; 12-TPI; 16-TPI; 20-TPI; 28-TPI; and 32-TPI. When a fixed series coincides with: C; F; or EF, the C; F; or EF take precedence.

Appended to the UN are several suffixes: C = Coarse; F = Fine; EF = Extra Fine; For ease of design, and improved size standardization, the writers of the ANSI B1.1 standard have established the Coarse, Fine and Extra Fine standardized series. Thus, if a design requires a coarse thread, the nominal major diameter is selected and then the coarse thread for that size can be identified within the standard and used in the design. Similar for fine and extra fine requirements.

In addition to the standard series above, appended to the UN may be the suffix: S = Special. The S is used when a thread is designated which does not meet any of the above parameters. It is used for unique nominal-major-diameter/thread-per-inch combinations. Whenever possible, do not design using a UNS special series thread. Stay with the Coarse, Fine, and Extra Fine series in new designs.

Sometimes added to the above designations is: R. The R designation is only appropriate to be used on external screw thread. The R designation is used to designate threads which have a controlled root radius. This is a smaller radius than the J-series mentioned next. The R is always added or inserted right after: UN. There will never be both an R and a J in the same designation.

Also sometimes added to the above designations, except the R, is: J. The J designation is used to designate threads which are modified to meet the requirements of ANSI/ASME SAE AS8879 (formerly MIL-S-8879). The J is always added or inserted right after: UN. For some sizes, ANSI/ASME SAE AS8879 also adds an S after the J; it will not replace C, F or EF.

Application of the above designation system as it relates to 3/4” threads:

For 3/4” UN the sizes available are: 3/4”-12 UN; 3/4 ”-28 UN and 3/4”-32 UN. Note that: 4; 6; 8; 16; and 20 threads-per inch are not listed. The very coarse: 4; 6; and 8 are too coarse to be practical for a thread of 3/4". The 16-TPI series is overridden by the Fine series. The 20-TPI series is overridden by the Extra Fine series.

For 3/4” UNC the only size is 3/4”-10 UNC.

For 3/4” UNF the only size is 3/4”-16 UNF. Note that the Fine series has over ridden the UN fixed designation.

For 3/4” UNEF the only size is 3/4”-20 UNEF Note that the Extra Fine series has over ridden the UN fixed designation.

For 3/4” UNS the sizes are any other that you can combine, other than those mentioned above. Some common special series combinations are: 3/4”-14 UNS; 3/4”-18 UNS; 3/4”-24 UNS; 3/4”-27 UNS.

COMMENTS
Refer comments/corrections to gageguy@gagecrib.com.
Originally published: May 12, 2009

About UsUsed SurplusTech InfoCatalogsContact UsBookmarkSitemap
 

 

Top

Gage Crib Worldwide, Inc.
6701 Old 28th St SE, Suite B
Grand Rapids, MI 49546-6937
Phone: 001-616-954-6581 • Fax: 001-616-954-6583
Email: gageguy@gagecrib.com

Copyright © 2002-2012 Ring & Plug Thread Gages. All rights reserved.