The metal d-645mw is part of the hitec d-series dynamo servo line. All hitec d-series servos have been designed using brand new, cutting edge, custom engineering. Combining industry leading high-resolution, state-of-the-art ultra-response technology with a 32-bit mcu and 12-bit adc for unprecedented programmability and flexibility, these servos deliver significantly smoother movement. The speedy, powerful line operates on a wide 4. 8 ~ 8. 4 voltage range, allowing use with any common battery chemistry without the need for adapters or regulators. Featuring hitec s industry standard 25-tooth output spline with 3mm hex screw, each d-series servo brings monster performance never known before in the market.