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Repair Center  How to Buy a Compatible Trimmer Head

Why Read This Article?

  • Steps to find a compatible trimmer head.
  • Bolt dimensions explained.
  • Threaded hardware syntax examples.

Article Breakdown

  • Trimmer head compatibility shopping is similar for most trimmers.
Match the Trimmer Head Arbor Bolt
  • The arbor bolt is the most major compatibilty issue for trimmer heads.
  • Match the trimmer head exactly to the correct arbor bolt whenever possible.
Threaded harware Dimension Syntax
  • Arbor bolt diameter and thread count must be known in order to make a match.
These dimmensions follow standard syntax for trimmer head arbor bolts:
  • [bolt diameter (in inches)] - [# of threads per inch]
  • [bolt diameter in (millimeters)] x [width of threads (in millimeters)]
Arbor Bolt Gender and Rotation
The gender and rotational direction of the arbor bolt must be matched too:

1. genders must be opposite

2. rotational directions must be the same The abbreviations for these variable are as follows:

  • LHF (Left Hand Female)
  • RHF (Right Hand Female)
  • LHM (Left Hand Male)
  • RHM (Right Hand Male)
Trimmer Head Bolt Adapters
  • Almost any trimmer head can be made compatible to a trimmer with the right bolt adapter.
  • Check to see if the trimmer head you're interested in has a bolt adapter that will fit your trimmer.

How to Buy a Compatible Trimmer Head

This article explains how to match a new trimmer head a trimmer by comparing arbor bolt and adapter specifications.
Trimmer heads are designed to be easily removed from their trimmers, and the many different trimmer heads on the market even outnumber the hundreds of trimmer models available. 
New trimmer heads often need to be purchased to replace broken heads, but their easy installation and low expense make it convenient for users to buy a new head just to upgrade or change trimmer features.
(Note: Owners of corded electric trimmers should be aware that the vast majority of corded electric trimmers are designed to use only the trimmer head with which they come. This means that an exact parts match for that model should be found in the event of a replacement.)

Trimmer Head Choosing new a trimmer head's line type, feed type, and other features will be different for every shopper and application, and mostly boil down to user preference. However, compatibility shopping is similar for almost all types of trimmer heads.
The information below discusses the measurements and specifications that help shoppers find a matching trimmer head for their trimmer.
  Match the Trimmer Head Arbor Bolt
The major compatibility issue for a trimmer head is the bolt that attaches it to a trimmer, called the arbor bolt. A trimmer head's arbor bolt is at the center of the trimmer head, and can be either male or female, depending on the "gender" of the receiving bolt on the trimmer.

Trimmer Head Arbor Bolt If you know the arbor bolt dimensions that your trimmer head needs to have to match the receiving bolt on its trimmer, the easiest way to shop for compatibility is simply to buy a trimmer head with the exact bolt you need.   Threaded Hardware Dimension Syntax
The diameter and thread count of a new trimmer head's arbor bolt must match those of the receiving bolt on the trimmer. Trimmer heads are usually advertised and listed with a short string of measurements that describe the dimensions of its arbor bolt. These measurements almost always follow a standard syntax for threaded hardware, and can be in English standard measurements or metric.
Each syntax is shown below with an example:

English Standard Syntax:

[bolt diameter (in inches)] - [# of threads per inch]

Example: 3/8"-25

Meteric Syntax

[bolt diameter in (millimeters)] x [width of threads (in millimeters)]

Example: 10mmx1.5
There is a third portion to this syntax (for other threaded hardware) that describes length, but the length portion of the syntax is usually left out of trimmer head arbor bolt information because their length is fixed.
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  Arbor Bolt Gender and Rotation
So far, we've explained two trimmer head arbor bolt measurements that shoppers need to match (diameter and thread count), but there are still two specifications to go. The gender of the trimmer head arbor bolt and the rotational direction of its threads must also be matched correctly.
The gender and rotational direction of a trimmer head arbor bolt are determined by what type of receiving bolt (male/female, left hand/right hand rotation) is on the trimmer.
Here are two guidelines:

1. The gender of the trimmer head arbor bolt must be the opposite of the receiving bolt on the trimmer.

2. The rotational direction of the bolts must be the same on both bolts. So, for example, a left hand rotation, female receiving bolt on a trimmer needs a trimmer head with a left hand rotation, male arbor bolt. And a trimmer with a right hand rotation, male receiving bolt needs a trimmer head with a right hand rotation, female arbor bolt. Of course, diameter and thread count must match exactly in both examples.
Gender and rotation are usually abbreviated as shown below, and in the case of trimmer head arbor bolts, the abbreviations usually follow the other arbor bolt specifications in the syntax:

  • LHF (Left Hand Female)
  • RHF (Right Hand Female)
  • LHM (Left Hand Male)
  • RHM (Right Hand Male)

Examples: 3/8"-25LHF or 10mmx1.5RHM (both are common arbor bolt sizes)
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Trimmer Head Bolt Adapters
As discussed above, there are four trimmer head arbor bolt specifications that must be matched when shopping for a compatible trimmer head: diameter, thread count, gender, and rotational direction. Although it is always extremely helpful to understand the ins and outs of these measurements and their syntax, manufacturers often make trimmer head compatibility easier by including bolt adapters. Almost any trimmer head can be made compatible to almost any trimmer with the right arbor bolt adapter. Bolt adapters can change any or all of the four trimmer head arbor bolt specifications. That is to say they can convert between diameters, thread sizes, gender, rotational direction, and any combination of the four.

Arbor Bolt Adapters Trimmer heads often come with one or more bolt adapters, sometimes an entire set. This makes it easier for manufacturers to market their trimmer heads to many trimmer models. If the trimmer head that you're looking at does not have an exactly matching arbor bolt, check to see if it comes with a bolt adapter that makes it compatible to your trimmer model.
Bolt adapters use the same measurement, gender, and rotation syntax as arbor bolts, and they are almost always listed with the trimmer head's other specifications (if included).
Adapter bolts can be found separately as well, so if you've found a trimmer head that you really like, don't give up on it right away if it doesn't come with the exact arbor bolt that you need for your trimmer. [Back to top]   Conclusion
Out inventory here at eReplacementParts.com is stocked with thousands of power tool accessories, including trimmer heads. Visit our Trimmer Heads page to find a part that matches your trimmer.
Click on the arbor bolt specification that matches your trimmer at the top of the page, and the page will refresh to show only those trimmer heads that match!
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