Full explanation
ISO 500-1/2/3 standards define PTO geometry: 6-spline (1 3/8 inch) for 540 rpm up to 75 HP; 21-spline (1 3/8 inch) for 1,000 rpm up to 130 HP; 20-spline (1 3/4 inch) for 1,000 rpm 130–300+ HP. Economy mode 540E/1000E runs the engine at lower rpm for light loads, saving 8–15% fuel. Critical: match PTO speed (540 vs 1,000) to implement — rotary mower 540, large spreader 1,000. PTO injuries are among the most common in farming: PTO guards are mandatory; damaged guards require immediate replacement. Front PTO powers front-mounted implements. Trade-off: PTO-powered implements require cardan shafts with U-joints — efficient but require regular lubrication (every 8–50 engine hours).