A strong auto-feed string trimmer advances line without bumping and matches its power source and cutting width to your yard; the MZK 20V Cordless Weed Wacker is a strong fit for buyers who want a cordless 12-inch tool with an 8000 RPM motor. This lineup includes cordless 20V and 40V options, a 6.5-amp corded model, and trimmer-edgers that can help finish lawn borders. Auto-feed systems are not all alike: some advance line during operation, while the WORX WG163 uses a push-button command feed rather than automatic feed.
Check what comes in the box, too; several products list a battery and charger, while others have different included components or limited specification details. The comparisons below prioritize feed type, stated cutting dimensions, and useful included equipment.
The MZK 20V Cordless Weed Wacker leads this group because it combines automatic line feed with an 8000 RPM motor, a 12-inch cutting diameter, and a stated weight of 6.3 pounds. Its cordless design and adjustable handle suit buyers who want to maneuver around a typical lawn without a cord. For a wider cut and edging conversion, the BLACK+DECKER BESTA510 provides a 14-inch path and wheeled edger function, but it requires a cord.
Choose based on power source, feed mechanism, and the specific yard tasks you need to cover.
Our Top Picks
Best OverallIts automatic line feed, 8000 RPM motor, and 12-inch cutting diameter give it a strong combination of stated performance and convenient cordless operation.
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Best Battery KitAuto feed, variable-speed control, a 12-inch dual-line path, and an included 2.0 Ah battery and charger make this a well-equipped cordless option.
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Best Corded OptionIts 6.5-amp motor, 14-inch cutting width, automatic feed spool, and wheeled edger conversion suit buyers prioritizing coverage and lawn-edge finishing.
View on Amazon- Best 20V Edger BLACK+DECKER LST300
Compare Auto-Feed String Trimmers by Power and Features
| # | Product | Dimensions L x W | Weight | Size | Buy |
|---|---|---|---|---|---|
| 1 | 1. MZK 20V Cordless Weed WackerBest Overall | 17.32"L x 6.69"W | — | 12 | View on Amazon |
| 2 | 2. Greenworks 40V String TrimmerBest Battery Kit | 12"L x 0.65"W | 12 lb | 12" (Battery Included) | View on Amazon |
| 3 | 3. BLACK+DECKER BESTA510Best Corded Option | 8.5"L x 4.88"W | 6.3 lb | One Size | View on Amazon |
| 4 |  4. BLACK+DECKER LST300Best 20V Edger | 36.23"L x 8.5"W | 5.7 lb | One Size | View on Amazon |
| 5 |  5. Boltarc 21V Weed WackerCordless three-in-one shoppers | 47.16"L x 6.28"W | — | — | View on Amazon |
| 6 |  6. WORX WG163Sloped-ground edging control | 44.6"L x 35"W | 5.5 lb | 20V GT 3.0 Trimmer / Edger | View on Amazon |
Detailed Reviews: Best Auto Feed String Trimmer
#1 · Best Overall
1. MZK 20V Cordless Weed Wacker
- Dimensions L x W: 17.32"L x 6.69"W
- Size: 12
Best for: Lightweight high-speed cordless trimming.
Why it ranks #1: Its automatic line feed, 8000 RPM motor, and 12-inch cutting diameter give it a strong combination of stated performance and convenient cordless operation.
An 8,000-RPM motor gives the MZK ET2307 a clearly stated high-speed specification for trimming grass and weeds, while its 12-inch cutting diameter covers ground with each pass. Automatic line feed removes manual line advancement, and the listed 4.0Ah battery completes this cordless package.
The 12-inch cutting diameter provides a defined coverage width for routine trimming, while automatic line feed releases string without manual operation, supporting a smoother workflow. MZK lists an 8,000-RPM motor for grass and weed cutting and a 4.0Ah battery with the cordless tool. Its 6.3-pound weight and adjustable handle are practical handling details: the listed light weight and ability to adjust the handle can help when maneuvering around lawn edges and landscaping.
- 8,000-RPM motor listed for grass and weed trimming
- 12-inch cutting diameter
- Automatic line feed releases string without manual operation
- 4.0Ah battery and 6.3-pound listed weight
- The supplied details do not state a runtime for its 4.0Ah battery.
Skip it if you need a stated operating duration before choosing a cordless trimmer; this listing gives battery capacity but no runtime figure.
The MZK suits buyers seeking a lightweight cordless trimmer for grass and weeds, with auto feed and a 12-inch path. Its listed 4.0Ah battery is useful context, but runtime is not specified in the supplied details.
Full product details
| Brand | MZK |
|---|---|
| Color | red |
| Item Dimensions L x W | 17.32"L x 6.69"W |
| Manufacturer | MZK |
| Part Number | ET2307 |
| Model Number | ET2307 |
| Dimensions | 17.32"L x 6.69"W |
| Size | 12 |
Listed on Amazon as: MZK 20V 12-Inch Cordless Weed Wacker, 8000 RPM, 4.0Ah Battery
View on Amazon#2 · Best Battery Kit
2. Greenworks 40V String Trimmer
- Dimensions L x W: 12"L x 0.65"W
- Weight: 12 lb
- Size: 12" (Battery Included)
Best for: Adjustable-speed cordless trimming.
Why it ranks #2: Auto feed, variable-speed control, a 12-inch dual-line path, and an included 2.0 Ah battery and charger make this a well-equipped cordless option.
Variable-speed control lets the Greenworks 40V trimmer adjust power to the task, giving lawn owners a way to tailor operation while trimming grass and light weeds. Its auto-feed system advances line without bumping, and the included 2.0 Ah battery and charger complete the cordless package.
A 12-inch cutting path with 0.065-inch dual line is specified for consistent trimming around lawns, sidewalks, and landscaping, making the coverage and line setup clear before choosing. Auto feed advances line during operation, avoiding bumping interruptions. The variable-speed trigger allows power adjustment for different tasks, while the included battery and charger mean the listed kit has its power components. At 12 pounds, its stated weight is worth considering if maneuverability is a priority during longer sessions.
- 40V cordless trimmer with 2.0 Ah battery and charger
- 12-inch cutting path with 0.065-inch dual line
- Auto-feed system advances line during operation
- Variable-speed trigger adjusts power to the task
- At 12 pounds, it is heavier than the listed 5.5-pound WORX WG163.
Skip it if you prioritize a lighter listed weight for maneuvering; the WORX WG163 is listed at 5.5 pounds versus this Greenworks trimmer’s 12 pounds.
Pick this Greenworks for cordless lawn work where a 12-inch dual-line path, auto feed, and adjustable speed suit the task. Its listed 12-pound weight is an important consideration for buyers focused on easier handling.
Full product details
| Brand | Greenworks |
|---|---|
| Color | Dark Green 12" |
| Included Components | String trimmer^battery^charger^instruction manual |
| Item Dimensions L x W | 12"L x 0.65"W |
| Item Weight | 12 pounds |
| Manufacturer | Greenworks |
| Part Number | 2101602 |
| Manufacturer Warranty Description | 2 Year |
| Model Number | 2101602 |
| Size | 12" (Battery Included) |
| Style Name | String Trimmer |
| Additional Information | Important Information Proposition 65 Warning for California Consumers WARNING: This product can expose you to chemicals including lead which is known to the State of California to cause cancer and birth defects or other reproductive harm. For more information go to www.P65Warnings.ca.gov |
Listed on Amazon as: Greenworks 40V 12 in Cordless String Trimmer, 2.0 Ah Battery and Charger
View on Amazon#3 · Best Corded Option
3. BLACK+DECKER BESTA510
- Dimensions L x W: 8.5"L x 4.88"W
- Weight: 6.3 lb
- Size: One Size
Best for: Corded lawn-edge finishing.
Why it ranks #3: Its 6.5-amp motor, 14-inch cutting width, automatic feed spool, and wheeled edger conversion suit buyers prioritizing coverage and lawn-edge finishing.
Its wheeled edge guide lets this 6.5-amp BLACK+DECKER switch from trimming to edging by rotating the tool, making it a practical pick for homeowners who want both jobs covered. Automatic Feed Spool advances line without bumping, while the 14-inch cutting width handles lawn edges and overgrowth.
The 6.5-amp motor and POWERDRIVE transmission provide the stated power for tackling tough weeds, grass, and overgrowth, while the 14-inch cutting width covers a useful strip with each pass. Rotate the tool to use the wheeled edge guide for borders along sidewalks, driveways, and flower beds. Automatic Feed Spool keeps line moving without bumping, and the included spool, guard, and auxiliary handle provide the listed essentials for setup and operation. At 6.3 pounds, it is a lightweight corded option.
- Automatic Feed Spool advances line without bumping
- Wheeled edge guide supports edging after rotating the tool
- 6.5-amp motor with POWERDRIVE transmission
- 14-inch cutting width and 6.3-pound listed weight
- Its electric design is corded, so operation depends on a power connection.
Skip it if you need a cordless setup for trimming away from a power connection; the BLACK+DECKER LST300 is a listed battery-powered alternative.
Choose this for lawn trimming and wheeled edging around paths or flower beds when you can work with a corded electric tool. Its 14-inch path and automatic feed suit routine overgrowth, while access to power is the key fit consideration.
Full product details
| Brand | BLACK+DECKER |
|---|---|
| Color | Orange, Black |
| Included Components | (1) BESTA510 String Trimmer(1) AF-100 Spool(1) Auxiliary Handle(1) Guard |
| Item Dimensions L x W | 8.5"L x 4.88"W |
| Item Weight | 6.3 pounds |
| Manufacturer | BLACK+DECKER |
| Part Number | BESTA510 |
| Manufacturer Warranty Description | 2 Year Limited Warranty, 30 Day Money Back Guarantee |
| Model Number | BESTA510 |
| Size | One Size |
| Style Name | String Trimmer |
| Additional Information | Important Information Proposition 65 Warning for California Consumers WARNING: Cancer and Reproductive Harm – www.P65Warnings.ca.gov Proposition 65 Warning for California Consumers WARNING: Cancer – www.P65Warnings.ca.gov |
Listed on Amazon as: BLACK+DECKER Weed Wacker with Auto Feed, 14-Inch 2 in 1 String Trimmer Lawn Edger, Powerful 6.5-Amp Lightweight Electric Weed Eater (BESTA510)
View on Amazon#4 · Best 20V Edger
4. BLACK+DECKER LST300
- Dimensions L x W: 36.23"L x 8.5"W
- Weight: 5.7 lb
- Size: One Size
Best for: Battery-powered trim and edging.
Why it ranks #4: Automatic spool feed and a 12-inch cutting width come with a 20V battery and charger, plus quick conversion between trimming and edging.
Its included 20V MAX battery and charger make this BLACK+DECKER LST300 a ready-to-use cordless trimmer and edger kit. The 2-in-1 tool converts between trimming and edging, while Automatic Feed Spool advances line as needed without bumping, helping simplify routine lawn-edge work.
The POWERDRIVE transmission sends more power from the motor to the cutting string, and the listed 6,200 RPM supports faster cutting work according to the product details. Switch between trimming and edging in seconds to handle both lawn growth and borders with one tool. The included 20V MAX battery, charger, AF-100 spool, and guard make this a kit rather than a bare tool. Its 12-inch width and 5.7-pound weight offer concrete fit cues for navigating smaller lawn areas.
- 20V MAX battery and charger included
- Automatic Feed Spool advances line without bumping
- Converts between trimming and edging
- 12-inch cutting width and 5.7-pound listed weight
- Its 12-inch cutting width is narrower than the 14-inch BLACK+DECKER BESTA510.
Skip it if you want a wider cutting path for each pass; the BLACK+DECKER BESTA510 lists a 14-inch width compared with this trimmer’s 12 inches.
This fits buyers who want a cordless kit for trimming and edging without gas, with battery and charger included. Choose it for a 12-inch path; shoppers prioritizing wider coverage should account for that limit.
Full product details
| Brand | BLACK+DECKER |
|---|---|
| Color | Orange, Black |
| Included Components | Included Components: LST300 20V MAX* Cordless Trimmer/Edger, (1) LBXR2020 20V MAX* lithium ion battery, (1) Charger, (1) AF-100 Spool, (1) Guard |
| Item Dimensions L x W | 36.23"L x 8.5"W |
| Item Weight | 5.7 pounds |
| Manufacturer | Black & Decker Outdoor |
| Part Number | LST300 |
| Manufacturer Warranty Description | 2 year limited warranty |
| Model Number | LST300 |
| Recommended Uses | Edging |
| Size | One Size |
| Style Name | 20V String Trimmer Kit |
| Additional Information | Important Information Proposition 65 Warning for California Consumers WARNING: Cancer and Reproductive Harm – www.P65Warnings.ca.gov |
Listed on Amazon as: BLACK+DECKER 20V MAX String Trimmer and Edger 2 in 1, Cordless Weed Wacker with Auto Spool Feed, Battery and Charger Included, 12 Inch Steel Deck, Reduced Vibration (LST300)
View on Amazon#5
5. Boltarc 21V Weed Wacker
- Dimensions L x W: 47.16"L x 6.28"W
Best for: Cordless three-in-one shoppers.
Why it ranks #5: The title identifies a cordless 21V, 3-in-1 auto-feed trimmer, but the supplied specifications provide little detail about cutting width or included battery equipment.
A 21V cordless format paired with auto-feed line is the defining combination on Boltarc’s RT-01, giving buyers a trimmer listing that promises automatic line advancement without a cord. Its title also calls it a 3-in-1 weed wacker, a useful starting point for shoppers seeking multiple functions in one tool.
The listing identifies the RT-01 as a 21V cordless weed wacker, so its stated power format suits buyers looking for a tool not tethered by a power cord. Auto-feed string is the other named feature; it signals automatic line advancement rather than a manual feed step. The title’s 3-in-1 description may attract shoppers consolidating yard tasks, but the supplied details do not specify the three functions, cutting width, battery capacity, included accessories, or operating weight.
- 21V cordless designation
- Auto-feed string listed in the title
- 3-in-1 designation for shoppers seeking multiple functions
- RT-01 model identification
- The supplied product details do not explain what the three functions are.
Skip it if you need a stated cutting width, battery capacity, or described edging conversion; the WORX WG163 lists a 12-inch width and trimmer-to-edger conversion.
Consider the Boltarc RT-01 if a cordless 21V tool with auto-feed and a 3-in-1 label matches your shortlist. The supplied information leaves the three functions and key operating specifications unspecified, so those details are a meaningful fit boundary.
Full product details
| Brand | Boltarc |
|---|---|
| Color | Dark Green |
| Item Dimensions L x W | 47.16"L x 6.28"W |
| Manufacturer | Boltarc |
| Part Number | RT-01 |
| Model Number | RT-01 |
| Dimensions | 47.16"L x 6.28"W |
Listed on Amazon as: 21V Cordless Weed Wacker Eater, 3-in-1 Auto Feed String Trimmer
View on Amazon#6
6. WORX WG163
- Dimensions L x W: 44.6"L x 35"W
- Weight: 5.5 lb
- Size: 20V GT 3.0 Trimmer / Edger
Best for: Sloped-ground edging control.
Why it ranks #6: It converts between trimming and edging and includes batteries, but its push-button command feed is not automatic line feed, making it a weaker keyword match.
A head that tilts 90 degrees helps the WORX WG163 reach sloped terrain and difficult spots, while its rubberized wheels guide straighter edging lines. This 20V cordless tool also converts between trimming and edging in seconds, joining two lawn tasks in one package with battery and charger included.
The Command Feed spool system supplies line at the press of a button, giving users direct control over line release instead of relying on bumping. For edging, the rubberized wheels guide the tool and the 90-degree tilting head accommodates slopes and hard-to-reach areas. The trimmer converts to an edger in seconds, and the package lists two batteries, a charger, edger wheel, safety guard, and flower guard. Its 5.5-pound listed weight supports a lighter-handling setup.
- Head tilts 90 degrees for slopes and hard-to-reach places
- Rubberized wheels guide straighter edging
- Push-button Command Feed supplies line on demand
- Two batteries and charger included; listed weight is 5.5 pounds
- Line advances by push-button command rather than automatically feeding during operation.
Skip it if you want line to advance automatically as you trim; the Greenworks 2101602 lists an auto-feed system for operation.
Choose the WG163 for a cordless trimmer-edger that can follow sloped ground and guide borders with wheels. Its push-button line feed suits buyers who want control, but not those seeking automatic line advancement.
Full product details
| Brand | WORX |
|---|---|
| Color | Black and Orange |
| Included Components | Trimmer, safety guard, flower guard, charger, battery (2) pack, edger wheel, spool, spool caps |
| Item Dimensions L x W | 44.6"L x 35"W |
| Item Weight | 5.5 pounds |
| Manufacturer | Positec Technology (China) Co., Ltd |
| Part Number | WG163 |
| Model Number | WG163 |
| Recommended Uses | Edging, Trimming |
| Size | 20V GT 3.0 Trimmer / Edger |
| Style Name | 2 in 1 Trimmer w/(2) Batteries & 0.4 Ah Charger |
Listed on Amazon as: WORX 20V 12" 2-in-1 Cordless String Trimmer & Electric Lawn Edger, WG163
View on AmazonAuto feed does not mean every trimmer feeds the same way
Auto feed is not interchangeable with a button-operated feed system, so check how line advances before choosing. The MZK, Greenworks, and BLACK+DECKER models explicitly describe automatic feed or an automatic spool that advances line without bumping. By contrast, the WORX WG163 advertises Instant Line Feed through a push-button command; that gives the user control but is not the same hands-off operation.
A practical mismatch can be frustrating: someone expecting the line to advance automatically may stop work to operate the WORX feed button. The Boltarc title says auto feed, but the supplied data does not explain its feed mechanism in detail.
If feed behavior is your priority, favor products with a clear description of automatic advancement, and treat vague listing details as a reason to verify the manual or compatibility information before purchase.
Check replacement-line details before buying
Confirm the spool and line type for the exact model before ordering replacements; these listings do not establish universal compatibility. The BLACK+DECKER BESTA510 and LST300 both list an AF-100 spool among included components, while the Greenworks trimmer specifies a 0.065-inch dual-line system. Those details are useful starting points, but they do not prove that one model’s spool fits another brand or model.
The WORX WG163 uses a command-feed spool system and mentions free spools, but the supplied information does not give a line diameter. The MZK listing describes automatic spool operation without naming a replacement spool specification.
A common buying trap is assuming that similar cutting widths mean compatible line or spools. Match replacements to the manufacturer’s model-specific instructions, especially when a listing omits diameter or spool identifiers.
How to Choose an Auto-Feed String Trimmer
Feed mechanism
Look for explicit automatic advancement if you want line to feed without bumping or pressing a control. The MZK, Greenworks, BLACK+DECKER BESTA510, and BLACK+DECKER LST300 describe automatic feed; the WORX WG163 instead uses a push-button command feed. Boltarc’s title calls it auto feed, but the supplied specifications do not explain how the mechanism operates.
Buyers who want line to advance during work should favor the clearly described automatic systems. Gardeners who prefer to trigger each line release may find a command feed more suited to their routine, provided they are comfortable pressing the button.
When a listing gives little mechanism detail, verify the operating instructions before treating it as equivalent to an automatic spool.
Power source and included battery
Choose a corded or cordless model according to where you work and what equipment you already own. The BLACK+DECKER BESTA510 is a corded 6.5-amp trimmer, while the LST300 and WORX WG163 are 20V cordless models; Boltarc lists 21V, and Greenworks lists 40V with a 2.0 Ah battery and charger. MZK is a 20V cordless model with a 4.0Ah battery named in its title.
The LST300 and WORX list batteries and chargers among included components, and Greenworks does too. A corded tool can suit a yard where an outlet and cord reach are workable; cordless kits better suit buyers who want to avoid a trailing cord.
Check kit contents rather than assuming a battery is included.
Cutting width and lawn-edge functions
Compare cutting width and conversion features against the amount and type of trimming you do. The BLACK+DECKER BESTA510 has a 14-inch width and converts to a wheeled edger, while the Greenworks, LST300, WORX WG163, and MZK list 12-inch cutting widths or diameters. WORX also has a tilting head, rubberized guide wheels, and an edging conversion; both BLACK+DECKER models convert to edgers.
A wider stated path can suit buyers who want to cover open grass with fewer passes, while 12-inch models may be easier to place around tighter lawn borders. If you mainly tidy edges, prioritize a stated edger function and guiding features; if you mainly trim grass, focus on cutting width and the tool’s listed feed system.
Which Auto-Feed String Trimmer Should You Choose?
Choose the MZK 20V Cordless Weed Wacker if you want a 12-inch cordless model with automatic line feed, an 8000 RPM motor, and a stated 6.3-pound weight. For a battery-and-charger kit with variable speed and a 12-inch dual-line path, the Greenworks 40V String Trimmer is the stronger fit. Pick the BLACK+DECKER BESTA510 if a 14-inch cut, corded power, and wheeled edging matter more than cordless mobility.
The BLACK+DECKER LST300 offers a 20V battery kit and automatic feed in a trimmer-edger format. Consider the Boltarc 21V Weed Wacker only if its sparse specifications meet your needs after verification.
The WORX WG163 suits buyers who want an edging conversion and prefer to release line with a button rather than rely on automatic feed.
Frequently Asked Questions
How often should I replace the line in an auto-feed string trimmer?
Replace the line when it becomes too short to cut effectively, breaks repeatedly, or the feed system can no longer advance it as intended. The interval depends on trimming frequency, vegetation, and contact with hard surfaces. Check the trimmer’s instructions for line-loading steps and the recommended line type.
What replacement spool or line is compatible with each trimmer?
Compatibility depends on the exact model, and the supplied information does not specify replacement spool or line sizes. Check each trimmer’s manual or product information for compatible parts before buying. In particular, do not assume that spools or line from one model will fit another, even when both have auto feed.
How long do cordless trimmer batteries run under typical yard conditions?
The supplied information does not state runtime for these cordless trimmers, so a specific duration cannot be confirmed. Actual use can vary with vegetation, trimming technique, and operating conditions. Compare the battery details and runtime guidance for the exact model, and consider whether the included battery and charger meet your yard’s needs.
Which models can convert from trimming to edging?
The BLACK+DECKER BESTA510, BLACK+DECKER LST300, and WORX WG163 are identified as trimmer-edger or edging-conversion options. The BESTA510 also has a wheeled edger function, while the WORX releases line with a button rather than relying on automatic feed. Check each model’s instructions for conversion steps.
Should I choose a corded or cordless trimmer?
Choose cordless if avoiding a cord and maneuvering around the yard are priorities; the MZK and Greenworks are cordless options, as are the LST300 and WORX. Choose the corded BESTA510 if its 14-inch cutting path and wheeled edging function suit your tasks. Match the power source to how you work.
Final Words
For a cordless model with automatic feed, an 8000 RPM motor, a 12-inch cutting diameter, and a stated 6.3-pound weight, the MZK leads this group. The Greenworks suits buyers seeking a battery-and-charger kit with variable speed and a dual-line path. Choose the BESTA510 for a wider cut and wheeled edging if a cord works for your yard.
Verify the Boltarc’s sparse specifications, and choose the WORX if button-released line suits you.
