Overview
Designed as a direct-fit aftermarket replacement, this trimmer head assembly replaces cracked or worn bump-feed heads on compatible string trimmers. The bump knob mechanism is a high-wear component that sees impact on every tap, and replacing the entire head is often more effective than individual part replacement. This assembly comes ready to wind with trimmer line.
Key specifications
- Replacement bump-feed trimmer head assembly
- Tap-to-advance line feed mechanism
- Includes bump knob and internal spring
- Compatible with standard trimmer line diameters
Compatibility
This trimmer head is designed for Husqvarna string trimmers as listed above. Confirm the thread size and direction match your trimmer’s drive shaft before ordering.
Installation notes
Remove the old trimmer head by holding the drive shaft and unscrewing the head assembly. Clean the shaft threads before installing the new head. Tighten the new assembly hand-tight plus a quarter turn, then load trimmer line according to the directional arrows on the spool.
Common questions
Q: Will the 537338701 T25 Tap Advance Bump Knob fit my Husqvarna 128LDX trimmer head, or is it only for the 129RJ and 525iLXT?
Yes, this bump knob is used on T25-style Husqvarna trimmer heads and is compatible with models including the 128LDX, 129RJ, and 525iLXT listed for this part. The most important thing is that your machine is using the T25 head, since the knob is made specifically for that head design.
Q: My bump knob on a Husqvarna 223L is worn down and not advancing line well—will replacing just this 537338701 knob usually fix that?
If the knob is rounded off, cracked, or no longer engaging properly when tapped, replacing it often restores normal bump-feed operation. If the head still does not advance line after installation, check the spool, spring, and line routing inside the T25 head for wear or binding.
Q: Do I need any special tools to install the T25 Tap Advance Bump Knob 537338701 on my Husqvarna 324L, and is there anything I should inspect while changing it?
In most cases, this is a straightforward replacement and does not require special tools beyond what you’d normally use to open the trimmer head. While installing it, clean out any packed grass or debris and inspect the spool and spring so the new knob can move freely and feed line correctly.
