GWS Direct Drive 8x4 Propeller. GWS Direct Drive series props offer high efficiency and great value for your electric powered models. The center hole of the prop is designed for a 3mm shaft, and can be drilled out for a 1/8" (3.17mm), 4mm or 5mm shaft. According to the widely accepted Maximum RPM formula of 100,000/D for GWS DD series props, the 8x4 DD prop should not be used over 12,500 RPM.