SRM-225 String Trimmer Head

Key Features

• 30-Second "Easy-Load" Technology: The patented Speed-Feed 400 design allows you to reload the entire head with trimmer line in under 30 seconds without disassembling the housing or removing the spool.
• Dual-Line Bump Feed: Engineered for professional-grade reliability, providing instant line advancement with a light tap on the ground while the engine is at full throttle.
• Balanced High-RPM Design: Factory-balanced to reduce centrifugal vibration, which minimizes wear on the gear head bearings and significantly reduces operator hand fatigue.
• Reinforced Metal Eyelets: Features high-durability metal line exits that resist friction-induced heat, preventing the nylon line from "welding" to the head during heavy trimming.
• High-Impact Polymer Housing: Manufactured from specialized glass-reinforced nylon to withstand high-velocity impacts with rocks, curbs, and fence posts.

Replaces / Cross-Reference Part Numbers

• Echo: 99944200907, 99944200908
• Shindaiwa: 78890-21001, 28820-08001
• Other: X047000490, X047000491

Compatibility & Fitment

This "400" series head is the primary replacement for most professional-grade straight-shaft trimmers. Key compatible models include:

• Echo SRM Series: SRM-210, SRM-225, SRM-225i, SRM-230, SRM-2100, SRM-2110, SRM-265, SRM-266.
• Echo PAS Series (Pro Attachment): PAS-210, PAS-211, PAS-225, PAS-230, PAS-260.
• Shindaiwa T-Series: T195S, T220, T222, T230, T231, T242, T242X.
• Technical Fitment: Designed for straight-shaft trimmers utilizing the M10 x 1.25 LHF (Left Hand Female) arbor thread.

When to Replace

• Worn-Through Bump Cap: The center knob has ground down from pavement contact to the point where the internal spring is exposed or it no longer triggers the line release.
• Cracked Outer Shell: Visible stress fractures in the black housing, which can cause the head to shatter or become dangerously unbalanced at high RPMs.
• Loading Mechanism Jam: The internal eyelets no longer align with the arrows, or the twisting mechanism has become seized with dried sap and debris.
• Frequent Line Snapping: The metal eyelets are missing or deeply grooved, causing the trimmer line to snap off inside the head repeatedly.
• Excessive Vibration: The head has become structurally unsound or unevenly worn, putting undue stress on the gear head and drive shaft.

Installation Tips

• Left-Hand Threads: This head is Left-Hand Threaded. To install, turn the head Counter-Clockwise onto the gear head shaft.
• Lock the Shaft: Insert a small hex key or the factory locking pin into the gear head hole to hold the shaft stationary while you spin the old head off and the new one on.
• The Loading Arrow: To reload, rotate the top knob until the arrows on the knob align perfectly with the metal eyelets. Push your line straight through the head until it is even on both sides, then twist the knob to wind.
• Line Diameter: For the SRM-225, 0.095" line provides the best balance of durability and cutting power without over-stressing the engine.
• Soak Your Line: To extend the life of your trimmer line, soak it in water for 24 hours. Hydrated nylon is much more flexible and significantly less likely to snap at the eyelet during heavy use.