ScubaPro MK21 DIN First Stage Regulator Designed for Travel, the MK21 First Stage is 20% smaller than the MK25! A new compact, balanced piston-controlled first stage with exceptional SCUBAPRO breathing performance at a mid-range price. The high airflow delivery to the second stage ensures unaffected breathing effort, no matter the tank pressure or depth. Very good resistance to freezing for a compact first stage, due to the external fins which optimize thermal exchange. Compact in size(16mm smaller than the MK25) but not in features, this modern, striking first stage has a "smart" hose layout for perfect positioning and easy identification. The standard cap (+/- 20 degrees routing) can be replaced with an optional cap, which has 4-hose low-pressure routing configurations (0 degrees/30 degrees) and a 5th central High Flow LP port. AIR BALANCED FLOW-THROUGH PISTON Balanced-piston first stages are the first choice of demanding deep sport divers and professionals. First stages with air-balanced pistons deliver significantly more air to the second stage than any other first stage, while their performance is totally unaffected by changing tank pressure and depth. A balanced piston allows the use of lighter and more sensitive components, resulting in an ultra-fast breathing response, instant deliver of air on demand, and extra-high airflow, especially in low tan pressure ranges.