Lifter Action in an injection mold provides for the molding of undercuts.  The undercut can be internal or external on the part.  Typical parts are battery compartment covers on cell phones and calculators. The Lifter  also aids the ejection process.

Typical components in a lifter mold include:
    Lifter,  which forms the undercut and possibly the adjacent geometry and is attached to a blade, rod, arm etc.
    T-Coupling
    U-Coupling

    There are many different configurations of lifters made by  manufacturers.  Exploring Catalogs and websites can generate many ideas.  Unique lifters are common, and can aid in the ease of creating a design suitable for the undercut of a given part.

    Lifter angles typically do not exceed 28 degrees from the vertical, as exceeding 28 degrees causes a concern for wear.  Conversely, if the angle is on the small side (1-5 degrees), the travel required (if using ejection to move the lifter)  to release the part is a concern.