This fitting is a push in fitting so you just push the line in from both sides. It is mainly used where a stronger connection is required on a rigid port.One side is a standard 8mm (5/16) duotight push in fitting, where the other side is a compression adapted duotight (Screw Lock) for 1/4" / 6.35mm rigid fittings.This fitting also comes in a duotight 8mm x 8mm Screwlock.