The BS 1936 series discusses standards for undercuts and runouts for screw threads. BS 1936-2 is the second part of BS 1936 which covers the undercuts and runouts for both external and internal threads. BS 1936-2 gives recommendations for undercuts and runouts for high duty applications.
BS 1936-2 specifies requirements for dimensions for form, width and diameter of undercuts and runouts for ISO metric external and internal threads for use in general engineering applications. Threads may be cut or rolled without the die or tap fouling the component.
BS 1936-2 on screw thread runouts and undercuts is useful for:
An undercut of reasonable width allows threads to be cut on a component up to end without the end face of the screwing tool fouling the component. Design requirements are usually for a reasonable degree of control on the diameter at the root or crest of the undercut to avoid weakening the section at this point, and for a sufficient radius at the end of the undercut to avoid stress concentration. The production requirement is for an adequate width of undercut to allow the use of dies and taps with a reasonable throat angle or taper lead.
BS 1936-2 provides you with dimension specifications of undercuts and runouts for ISO metric external threads. BS 1936-2 also provides dimensions of runouts and undercuts for ISO metric internal threads. BS 1936-2 gives recommendations for lengths of runout for various angles of throat or taper lead.
BS 1936-2 guidelines help you to maintain standards for ISO metric screw thread runouts and undercuts.
ISO 3508:1976
ISO 4755:1983