Rotary # 6439 High Lift Lawn Mower Blade For 20" Cut For MTD # 942-0640 742-0640

What It Is

The Rotary #6439 is a high-lift replacement blade for 20-inch cutting deck walk-behind mowers, designed to increase suction for improved grass clipping discharge and bagging performance. It replaces MTD OEM part numbers 942-0640 and 742-0640.

Fitment & Compatibility

• Deck size: Only fits mowers with a 20-inch cutting width. Measure your deck before buying.
• Brand/model: Directly compatible with many MTD, Troy-Bilt, Cub Cadet, Yard Machines, and Yard-Man models using the OEM blades listed. Check your mower’s model number against Rotary’s fitment chart.
• OEM vs aftermarket: This is a direct aftermarket replacement for MTD factory blades. Fitment is identical, but blade thickness or material may differ slightly.
• Measurements: Center hole diameter is 7/8 inch. Overall length is 20 inches. Blade thickness is approximately 0.187 inch. Confirm these match your old blade.

Key Things to Know

• High-lift design creates more airflow than standard blades, which helps bag wet or thick grass but may bog the engine in tall, dense growth.
• Installation is straightforward: remove the center bolt, swap blades, and torque to 30–40 ft-lbs. Use a blade removal tool if the bolt is seized.
• Common gotcha: High-lift blades require a clean, sharp edge for best performance. Dull blades will strain the engine and reduce bagging efficiency.
• Balance check is recommended after installation—an unbalanced blade causes vibration and can damage the spindle.

Should You Buy It

Buy the Rotary #6439 if you have a 20-inch MTD-style mower and want better bagging or discharge performance, especially in normal to moderately thick grass. It’s a solid upgrade over standard OEM blades for the price, but avoid it if you frequently cut very tall or wet grass—the high lift may overload the engine.