The Apeks XL4 2nd Stage is a compact little second stage made for advanced divers who want a light weight mouthpiece that can handle colder waters. Based on the Flight 2nd stage the XL4 is small but powerful. Who's the XL4 2nd Stage For? Originally the XL4 was designed for technical divers who want a light, compact 2nd stage that won't create jaw fatigue or be bulky on a stage cylinder. Any Diver can appreciate the small XL4 for it's broad capabilities in being a cold water but lightweight 2nd stage. Fit to any length Standard Regulator Hose the XL4 is happy as a primary or alternate 2nd stage in either warm or cold water. Recommended Accessories The 2nd stage requires both a 1st Stage and a Regulator Hose to work properly & it's best if they are Assembled & Tested together because they may need adjusting so they balance & work correctly.