Designed to achieve the easiest operation and max performance again and again. The PRO .21/.28 Series have the most raw power & durability simultaneously! Of course, the new webbed reinforced compact crankcase is made for added wearing resistance and provides effective heat dispersion to meet the demands of long term usage. The PRO series are manufactured by automated computer-controlled machinery, using the highest quality materials. State-of-the-art CNC manufacturing techniques produce not only high performance and reliability but a product that looks and performs better. Precision mixture control carburetor makes adjustments simple. The crankshaft is lightened, and balanced to get a fuel mixture more smoothly. The .21/.28 engines fits in the same mounting space as the original .21/.28 engines, with no additional weight - but delivers greater output and higher practical rpm. All of series are available with built-in recoil starters ("X" type). The "D" type series engine features with dual starting system, recoil starter and rotor starter. The " K" type series engines feature a built-in hexagonal shaft starting system that can be operated to start the engine easily and quickly.