Base Extensions - Reduce Diameter - Euro Pin (EP) Reduce Diameter Base Extensions (RDM) or Skinny are the proper choice for use with Reduce Diameter Masts (RDM). RDM Euro Pin (EP) extensions are compatible with EP bases. We sell base extensions from: Chinook, Streamlined, and Epic. The Base Extension is used to achieve proper tension and luff length of sails. It has a pulley system and cleat to downhaul and secure tension. RDM or Skinny extensions have a diameter of 1..5" (approx 38cm). RDM base extensions come in 2 constructions: Aluminum or Carbon; are available in lengths: Short (6cm), Medium (28cm) and Tall (48cm).