128LD T25 Trimmer Head - Fits Husqvarna 124L, 125L, 128L, 128LD - Replaces 966674401

128LD Trimmer Head T25

Key Features

• High-Efficiency Tap 'N Go Feed: Specifically designed for entry-level and mid-range trimmers, the T25 head provides reliable line advancement with a simple tap on the ground, allowing for continuous operation without stopping.
• Easy-Reload Open Eyelets: Features a simplified spool design with open eyelets that make reloading trimmer line faster and less prone to tangling compared to traditional closed-loop heads.
• Reinforced Blue Bump Knob: The signature blue knob is manufactured from high-density, wear-resistant polymer to ensure a long lifespan even when used on abrasive surfaces like gravel or dry soil.
• Optimized Centrifugal Balance: Engineered to reduce vibration and shaft wobble, which protects the trimmer's flexible drive cable and reduces user fatigue during extended yard work.
• Pre-Wound Performance Line: Usually comes pre-loaded with premium 0.080" or 0.095" diameter line, offering an aggressive cut and high durability for residential trimming and edging.

Replaces / Cross-Reference Part Numbers

• 966674401
• 537338306
• 537338310
• 5373383-02
• 578446101

Compatibility & Fitment

This "T25" head is the standard replacement for Husqvarna's lightweight and consumer-grade straight-shaft trimmers. Key compatible models include:

• Husqvarna 120 Series: 122L, 124L, 125L, 125C, 125LDX, 128L, 128LD, 128LDX, 128R, 128RJ, 129L, 129LD.
• Husqvarna 200 & 300 Series: 223L, 223R, 322C, 323C, 325C, 325CX.
• Technical Specification: Fits models utilizing an M10 x 1.25 LHF (Left Hand Female) arbor thread.
• Note: While designed for straight-shaft trimmers, it is also compatible with specific Husqvarna curved-shaft models that use the M10 thread.

When to Replace

• Worn-Through Bump Surface: The blue center knob has ground down from pavement contact to the point where the internal spring is visible or the line no longer advances.
• Cracked Outer Housing: Visible fractures or chips in the black plastic shell, which can lead to the head shattering at high RPMs.
• Line Overlapping/Welding: The internal spool or divider is damaged, causing the line to melt together or jam inside the head during use.
• Eyelet Failure: The metal line exits (eyelets) are missing or have developed deep grooves, causing the trimmer line to snap off inside the head repeatedly.
• Excessive Vibration: The head is no longer balanced due to uneven wear, putting undue stress on the gear head and the trimmer's motor.

Installation Tips

• Left-Hand Threads: This head is Left-Hand Threaded. To tighten it onto the trimmer, you must turn the head Counter-Clockwise.
• 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.
• Spool Direction: When reloading line, follow the arrows molded into the internal spool. Winding the line in the wrong direction will prevent the Tap 'N Go mechanism from functioning.
• Soak Your Line: To extend the life of your trimmer line, soak the spool in water for 24 hours. This keeps the nylon flexible and much more resistant to snapping at the eyelet.
• Clean the Housing: Every time you reload the line, shake out any dirt or grass trapped inside the head to ensure the internal spring and spool move freely.