AS8879 PDF

The minor diameter of both external and internal threads provides a basic thread height of. The following detailed design requirements are included: a. Screw threads - UNJ basic profile and design profiles. Standard series of diameter-pitch combinations for nominal thread diameters from 0. Standard thread classes and form tolerances.

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AS REV. This standard has been revised to focus on the design requirements for screw threads — UNJ profile, inch. Procurement information not directly related to the design standard, such as product acceptance and quality assurance, have been removed. The use of this report is entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising therefrom, is the sole responsibility of the user.

SAE invites your written comments and suggestions. No part of this publication may be reproduced, stored in a retrieval system or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of SAE.

The minor diameter of both external and internal threads provides a basic thread height of. The following detailed design requirements are included: a. Screw threads - UNJ basic profile and design profiles. Standard series of diameter-pitch combinations for nominal thread diameters from 0. Standard thread classes and form tolerances.

Formulae for thread dimensions and tolerances. Method of designating UNJ threads. Tables for selected diameter-pitch combinations for close tolerance mechanical thread applications.

Tables for screw thread - UNJ profile thread limit dimensions. In addition, the purpose of this standard is to: a.

Define the geometric requirements for a selected series of Unified Screw Threads, modified to provide a radius at the external thread root. Establish requirements for a continuous radius at the root of the external threads. Establish requirements for an increase in the minor diameter of both internal and external threads to accommodate the external thread root radius.

The applicable issue of all publications shall be the issue in effect on the date of the purchase order. In the event of conflict between the text in this document and the references cited herein, the text in this document takes precedence.

Nothing in this document, however, supersedes applicable laws and regulations unless a specific exemption has been obtained. ASME B1. See Figures 1, 2 and 3 for illustrations of thread characteristics.

Standard UNJ threads shall be selected from those with diameter-pitch combinations listed in Tables 2 through 7. This table is provided for engineering reference only. Dimensions include pitch diameter, major diameter, minor diameter, and external thread root radius. Functional diameter Maximum Material shall be within pitch diameter limits.

The root radius radius of curvature tangent to the flanks shall be within the values given in Tables 2 through 7 see Figures 1 and 3. Several characteristics, which are provided as reference-only for Category 1 threads, are design requirements for Category 2 threads. However, the basic design profile and dimensions specified in Tables 2 through 7 and Table 9 are the same for both thread categories. Thread category shall be determined and specified with the thread designation on the drawing or referenced specification for threaded product in accordance with this standard.

When a thread category is not specified, Category 1 design requirements shall apply. Several design characteristics are reference-only for Category 1 threads. Category 2 Threads: The design characteristics for Category 2 threads are specified in Table 8. Limits of Size: Category 1 and Category 2 threads shall be within the limits of size specified in Tables 2 through 7. Note: Establishing conformance of a product thread for maximum and minimum material also establishes that the combined effects of these variations are within limits.

Variations, Category 2 Threads: Lead, flank angle, circularity roundness , taper, and runout are design requirements for Category 2 threads. This requirement applies only to full form threads.

Lead: The lead is the number of thread starts divided by the number of threads per inch. The variation in the lead including helix variation measured over a distance not less than the go ring gage blank as defined in ASME B Where product full form thread length is less than the gage blank length, the product thread lead variation is acceptable when functional diameter is within limits.

Flank Angle: The flank angle shall be 30 degrees. Runout: The circular runout of the external thread major diameter cylinder and the internal thread minor diameter cylinder with respect to the pitch diameter cylinder shall not exceed twice the pitch diameter tolerance. The root radius of the incomplete thread shall be greater than or equal to the minimum root radius listed in Table 1 and shall transition gradually onto the unthreaded portion.

There is no upper limit on root radius of incomplete threads as long as all other requirements are met. For parts with internal through threads, the incomplete runout threads shall not exceed 2 incomplete pitches. Incomplete Lead Threads: Unless otherwise specified, the entering end of external threads and internal threads may be outside the specified limits of size for a length not to exceed two pitches, including chamfer.

In no case shall the lead threads exceed the specified maximum material condition. Surface Roughness: On certain parts, it may be necessary to control the surface roughness of the thread flanks, roots, or crests.

This requirement shall be specified, if necessary, on the part drawing or specification. Surface roughness specifications should be commensurate with a realistic assessment of current production capabilities. For Category 1 and 2 threads, unless otherwise specified, the surface roughness of the thread flanks and the roots shall be no greater than 63? Where pitch diameter tolerance is 0. When circularity is checked using pitch diameter indicating gage segments or rolls, the circularity value is equal to one-half the difference between maximum and the minimum pitch diameter readings.

Threads 1. Circularity shall fall within the pitch diameter tolerance except above the 15 degree arc. The minimum pitch diameter before coating may be reduced by no more than 0. For threads with pitch diameter tolerance greater than 0. Unless otherwise specified, all external thread characteristics shall be within the adjusted dimensional requirements before coating or plating.

After coating or plating, the threads shall not exceed maximum material limits. Internal Threads: Unless otherwise specified, the minor diameter of internal threads to be coated or plated may be increased by 2 times the minimum plating or coating thickness. The maximum pitch diameter requirement may be increased by the same values as the reductions allowed for external threads. Unless otherwise specified, all internal thread characteristics shall be within the adjusted dimensional requirements before coating or plating.

Coating threads with Solid Film Lubricant: An adjustment of pitch diameter to accommodate the thickness of solid film lubricant is not in addition to that specified in 3. The product thread, before application of solid film lubricant, shall comply with AS dimensions.

When maximum and minimum material conformity cannot be accomplished on a completed screw thread product because of a configuration change to the threads e. Specify design category 1 or 2 when required. Omitting a category designation defaults to design category 1.

Special diameter-pitch combinations developed in accordance with this standard shall be designated as shown in the following examples. External Thread: 1. Mating the UNJ series external thread with the UN series internal thread should be avoided due to a potential interference at the minor diameter. For larger diameters, the constant pitch 12 thread per inch series is recommended see Table 6.

These tolerances are applicable for the lengths of engagement of these threads up to 1. These tolerances are applicable for lengths of engagement of these threads up to 15 pitches. Taps and thread gages for Class 3B. Minor diameter gages must meet the requirements of this standard. Thread gages for Class 3A, except crest truncation of the maximum material thread gage must be increased to 0. The cumulative variation of thread form deviations such as lead, flank angle, taper, and roundness is contained within the maximum- and minimummaterial limits.

Gaging elements for determining individual feature form deviations is not included in System System 23 Definition: System 23 is a group or set of gages that permit evaluation of functional size at the maximum-material limits within the length of the standard gaging elements, and also permits evaluation of the minimum-material size limits over the length of the full thread.

The System 23 group or set of gages includes those necessary for evaluation of thread form deviations such as lead, flank angle, taper, and roundness. An R symbol to the left of the document title indicates a complete revision of the document.

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