A plastic injection mold opens, closes and ejects the part in one direction or axis. Any detail of the plastic part that can not be released from the mold in the direction of this axis is considered an undercut. A mechanical device must be used to allow the release of this undercut detail in order for the mold to open, close and eject properly. A lifter is a mechanical device that moves parallel or relatively parallel to the directi on of the mold axis.

A spring loaded lifter is a lifter that uses a powerful die spring to open (release the undercut) and uses the closing of the mold to return it to the locked position.

A mechanical lifter is a lifter that uses the movement of the ejector system to open (release the undercut) and uses the closing of the mold to return it to the locked position. This is the most commonly used lifter mechanism.