Using a Circular Carbide Blade on Your Weed Whacker or String Trimmer

A Weed Whacker has various names: String Trimmer, Garden String Trimmer, Tree Pruner, Brush Cutter, Weed Eater, etc. As other articles have aptly pointed out, these versatile garden tools come with various cc-power levels, electric versus gasoline, and 2-stroke versus 4-stroke capabilities. But what has not been addressed is the use of a “BLADE” on such a tool for all the versatile work a blade can perform in the garden environment.


A circular saw Blade specifically made for and attached to a Weed Whacker gives the following versatility uses in the garden environment:

1. Tree trimming (aka Pruning) which in many cases actually works better than using a cumbersome heavy chain saw for pruning since the circular blade can be wielded at the end of a lighter longer 6 foot Weed Whacker shaft for reaching up into trees. Such a blade can typically cut a tree branch/ limb up to the diameter of the blade provided you cut from both sides of the limb.

2. A blade can be used for clearing large patches or even acreage of heavy thick wood stock brush and sticker brambles (aka: Blackberry sticker bushes) where a common string line spool would be much too weak to cut through adequately.

3. Hedge trimming is a dream with a blade attached to a Weed Whacker; the hedging action is faster and less jagged as compared to a standard hedging tool. So in conclusion, a blade attached to a Weed Whacker augments your common standard string trimmer into a full-on chain saw, hedge trimmer, and large acreage clearer of wood stock weed, saplings, and heavy tall growth brambles (ergo, Black Berry bushes).


Each Weed Whacker on the market is different and so each owner of their particular Weed Whacker will have to contact their respective Weed Whacker Manufacturer to inquire about BLADE attachment hardware. Most electric-powered versions are UNDER powered for handling a Blade so will probably NOT have blade attachment hardware available. On the other hand, most gasoline powered Weed Whacker’s will have Blade attachment hardware available. Blade attachment hardware normally consists of a standard blade guard along with a few small metal parts that fit on (slide onto) the little threaded shaft that the String Spool screws onto. These little pieces of hardware will consist of the lower part that will have a raised circle about the size of a common 25 cent piece (quarter) or as small as a nickel (5 cent piece). This raised circle is how the hole in the center of the Blade fits on, then the upper part hardware piece variously called “the cap piece” is applied on the top of the blade, then a nut that is screwed on top of the cap, followed by a cotter pin.

The hole in the blade is known as the ARBOR Hole. So it is important to know your “Arbor Hole” hardware diameter in order to match the blade’s Arbor Hole to your hardware when purchasing Blades for your Weed Whacker. The most standard Arbor Hole diameters in the industry are 1″, which is the same as 25.4mm, but also 20mm as well. From my experience I would say approximately 90% of all blades fit these two common ARBOR HOLE diameters. (Note: there are some Arbor Holes in these much lesser used diameters: 0.75in & 0.50in). SPECIAL NOTE: A table saw blade should never be used on a Garden String Trimmer as such blades are more brittle and built for only up to 3,450 rpm. Such blades can shatter when hitting a rock or something very hard which could be a safety concern not protected by the attached blade guard. Garden String Trimmer blades are specifically built for 10,000+ rpm and are manufactured with a more malleable flexible metal.


Blades typically come with steel teeth or CARBIDE teeth. Carbide is well worth considering since a Carbide Tipped (teeth) blade reputably can last up to 10 times longer than a standard steel blade but cost nowhere close to ten times more money. In fact, a Carbide tooth blade normally doesn’t even cost twice as much for 5 to 10 times the longevity over plain steel (maintaining sharpness for continued cutting power is the key to a blades value in relation to cost). It should be noted that Carbide is not really easily sharpened but steel can be. However, it should be also noted that the price of these steel blades makes them more of a throw away item once used up since the cost to re-sharpen (in time or money) is typically more than the cost of a new blade.


Standard Weed Whacker blades come in various styles:

1. THREE-PRONG or five-prong for simple soft green weed cutting. Each large prong has a cutting edge rather than actual teeth. The deeper inner most part of each prong does not often get the same cutting time as the outer edge part of each prong so dulling occurs in an imbalanced manner. This type of blade will not be suitable for pruning trees or hedging, nor for cutting heavy duty wood-stock type weeds, brush, or brambles. This type of blade is the cheapest and dulls the quickest since it spreads its cutting surface over only three to five cutting edges and only comes in basic steel, not carbide.

2. Thirty (30) to Forty (40) TEETH Blade: This is the next step up in Weed Whacker blade choices. Obviously 40 teeth offers substantially more aggregate cutting surface than the blade type mentioned above (3-prong). This type of blade is very adequate for cutting heavy stock weeds (e.g. tumble weeds), heavy thick brush and blackberry type sticker brambles but are not suitable for Pruning or Hedging. It should be added that these type blades must be sharp, otherwise the teeth tend to grab and tug wood stock weeds when dull. The reason Pruning and Hedging are not suitable for this type blade is too few teeth make this blade tend to seize inside green moist tree limbs when pruning and make it tend to tear and create jagged-tugging-yanking cuts on a hedge rather than smooth and attractive cuts. This type of blade normally comes in plain steel that dulls quickly but some are now available in carbide tipped teeth as well.

3. Eighty (80) to one hundred (100) TEETH Blade: This is the highest level in the Weed Whacker Blade choices. It should be clear now that the more teeth you have cutting, the more aggregate cutting surface area you are applying to the job at hand. In addition, an 80 tooth blade costs more money to make as compared to a blade with half as many cutting teeth as mentioned in (2) above (40 teeth). But the cost is not typically much more if at all for having 80 teeth over 40 teeth. The 80 plus teeth blade offers the most versatility, stays sharper longer and is the best value for the buck. The 100 teeth type blade is the absolute best value since if offers 25% more cutting surface area (teeth) over an 80 tooth blade.

The one main consideration is that the typical 80 tooth blade comes in 8 inch diameter that fits with the safety blade guard ON your Weed Whacker, and the 100 tooth type blade is normally 9 to 10 inch in diameter and therefore will not allow a blade guard to fit. We recommend that the maximum size diameter blade be limited to 9 inches unless you have a very powerful Weed Whacker, otherwise the large circumference of the largest blades can bog down the motor. So in conclusion: 8″ and 9″ diameter blades are best, offer the most aggregate cutting surface, therefore stay sharper longer, and offer the most versatility of jobs in the garden. NOTE: We think Carbide teeth are so worth the small extra purchase cost that we would say a 40 tooth carbide blade would be recommended over an 80 tooth plain steel any day of the week. But the 80 tooth or 100 tooth blade with Carbide Teeth is the absolute best there is.

Bill Brower

B & G International, LLC, Tacoma, Wa