Machinery's Handbook, 31st Edition
2012
Metric Screw Threads M Profile METRIC SCREW THREADS American National Standard Metric Screw Threads M Profile
American National Standard ANSI/ASME B1.13M-2005 (R2015) describes a system of metric threads for general fastening purposes in mechanisms and structures. The stan - dard is in basic agreement with ISO screw standards and resolutions, as of the date of pub - lication, and features detailed information for diameter-pitch combinations selected as to preferred standard sizes. This Standard contains general metric standards for a 60-degree symmetrical screw thread with a basic ISO 68 designated profile. Application Comparison with Inch Threads.— The metric M profile threads of tolerance class 6H/6g (see page 2019 ) are intended for metric applications where the inch class 2A/2B have been used. At the minimum material limits, the 6H/6g results in a looser fit than the 2A/2B. Tabular data are also provided for a tighter tolerance fit external thread of class 4g6g which is approximately equivalent to the inch class 3A but with an allowance applied. It may be noted that a 4H5H/4h6h fit is approximately equivalent to class 3A/3B fit in the inch system. Interchangeability with Other System Threads.— Threads produced to this Standard ANSI/ASME B1.13M are fully interchangeable with threads conforming to other Na - tional Standards that are based on ISO 68 basic profile and ISO 965/1 tolerance practices. Threads produced to this Standard should be mechanically interchangeable with those produced to ANSI/ASME B1.18M-1982 (Withdrawn) “Metric Screw Threads for Commercial Mechanical Fasteners—Boundary Profile Defined,” of the same size and tolerance class. However, there is a possibility that some parts may be accepted by conventional gages used for threads made to ANSI/ASME B1.13M and rejected by the Double-NOT-GO gages required for threads made to ANSI/ASME B1.18M. Threads produced in accordance with M profile and MJ profile ANSI/ASME B1.21M- 1997 (R2018) design data will assemble with each other. However, external MJ threads will encounter interference on the root radii with internal M thread crests when both threads are at maximum material condition. Definitions.— The following definitions apply to metric screw threads—M profile. Allowance: The minimum nominal clearance between a prescribed dimension and its basic dimension. Allowance is not an ISO metric screw thread term but it is numerically equal to the absolute value of the ISO term fundamental deviation. Basic Thread Profile: The cyclical outline in an axial plane of the permanently estab lished boundary between the provinces of the external and internal threads. All deviations are with respect to this boundary. (See Fig. 1 and Fig. 5.) Bolt Thread (External Thread): The term used in ISO metric thread standards to describe all external threads. All symbols associated with external threads are designated with lower case letters. This Standard uses the term external threads in accordance with United States practice. Clearance: The difference between the size of the internal thread and the size of the external thread when the latter is smaller. Crest Diameter: The major diameter of an external thread and the minor diameter of an internal thread. Design Profiles: The maximum material profiles permitted for external and internal threads for a specified tolerance class. (See Fig. 2 and Fig. 3.) Deviation: An ISO term for the algebraic difference between a given size (actual, mea sured, maximum, minimum, etc.) and the corresponding basic size. The term deviation does not necessarily indicate an error.
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