The Mk17 First Stage Regulator is the perfect choice for the recreational diver who wants the advantage of a diaphragm first stage for use in temperate waters. the C300 offers uncompromising breathing performance for avid recreational divers. The C300 is lightweight with an anti-scratch cover. The C300 allows all the adjustments options of a high-end regulator while remaining a mid-range system. Optimal Flow Design valve (OFD) is for reliable and high airflow.