The MK21 is SCUBAPRO's most compact balanced-piston first stage. Smaller and lighter than the MK25, it uses a smaller piston but it delivers the same level of breathing performance, no matter how hard you're breathing, how deep you're diving or what your pressure gauge reads. The MK21 also provides exceptional resistance to freezing due to the thermal exchange produced by the external fins on its polished chrome brass body.

The MK21's innovative "smart" hose layout comes with a standard cap with four low pressure ports angled ( /- 20º) to maximize hose routing. This standard cap can be replaced with an optional cap that offers four low pressure ports at more extreme angles (0°/30°) plus a fifth centralized high-flow low pressure port -- a useful configuration for technical diving.

• Air-balanced flow-through piston provides constant and effortless airflow unaffected by depth, tank pressure, or breathing rate.
• Polished chrome plated marine grade brass body is close to 20 percent smaller than the MK25, making it an easy travel companion.
• Unique thermal exchange design with external fins optimizes freezing resistance.
• Two high pressure ports, one on each side of the body, allows the first stage to be positioned either up or down.
• Standard "smart" hose routing cap offers four low pressure ports angled for more convenient hose routing ( /- 20º).
• Optional hose routing cap increases routing configurations with four angled low pressure ports  (0°/30°) plus a fifth centralized high-flow low pressure port, ideal for technical diving.
• Redesigned yoke allows for easier mounting on a cylinder, and redesigned cap protects internal components from water intrusion after the dive.
• Available in either 3364psi/232bar INT or 4350psi/300bar DIN configurations.
• Weight: INT 232 (oz/g): 27.5/780; DIN 300 (oz/g): 19.7/560.
• Airflow at 2900psi/200bar: (l/min/SCFM): >7500/265.
• Intermediate pressure (psi/bar): 133-142/9.2-9.8.