ASME-B18.3 Socket Cap, Shoulder, Set Screws, and Hex Keys (Inch Series)

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Socket Cap, Shoulder, Set Screws, and Hex Keys (Inch Series)


This Standard covers complete general and dimensional data for various types of hexagon socket cap screws, shoulder screws, set screws, and hexagon keys recognized as an American National Standard. Also included are appendices that provide specifications for hexagon socket gages and gaging, tables showing applicability of keys and bits to various socket screw types and sizes, drill and counterbore sizes for socket head cap screws, and formulas used for dimensional data. However, where questions arise concerning acceptance of product, the dimensions in the tables shall govern over recalculation by formula. Recess dimensions for Type VI recesses are given in Mandatory Appendix III.


Claudia's Notes:
This standard was originally developed by ASME in the 1930's and adopted as American Standards Association's (the precursor of ANSI) ASA B18.3, published in February 1936.  This new 2012 Edition replaces the previous ASME B18.3-2003 Edition, which is now obsolete.

Changes to the 2012 Edition are as follows:
Spline driven fasteners, and their associated keys, have been removed from the document and users that wish to use this type of fastener will need to refer to the previous edition. The Type VI (Six Lobe) drive style has been added as a mandatory appendix. The tolerance for protrusion requirements on flat head socket cap screws has been increased. An alternative method for measuring protrusion has been included and corresponds with the metric document ISO 10642.

Other less significant changes in this revision include the addition of some sizes and slight changes to the requirements for drilled heads.

To find similar documents by classification:

21.060.10 (Bolts, screws, studs)

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Document Number

ASME B18.3-2012

Revision Level




Publication Date

April 24, 2013

Page Count

64 pages