The Stem of a Pipe incorporates the air hole, Lip, Bit, and Tenon which connects to the Briar at the Shank; typically through Tenon and Mortise craftsmanship to ensure a tight and long lasting fit.    Stems vary in shape and nuance as much as the Pipes themselves.  Many great Pipe makers go to great lengths to ensure that their Stems are perfectly crafted to suit the pipes they serve.  Amber, Lucite, and Vulcanite are the most common materials for making Stems: these materials can be shaped easily and each have their respective pros and cons.