Parts of a Chainsaw and What Each One Does
Last updated October 31, 2026
The parts of a chainsaw fall into three groups: the powerhead with the engine or motor, handles and controls; the cutting attachment made up of the guide bar, saw chain and drive sprocket; and the safety group with the chain brake, front hand guard, chain catcher and throttle lockout. The powerhead makes the power, the cutting attachment turns it into a cut, and the safety group keeps the chain under control.
The bar does not cut. It guides the chain and carries oil to it, and the chain does the cutting.
How to read a chainsaw diagram
A side view of a gas saw reads from the cutting end to the handle end. At the front sits the guide bar with the chain wrapped around it, then the sprocket cover with the bar nuts, then the powerhead with the starter, the fuel and oil caps, and finally the rear handle with the trigger. The chain brake and the front hand guard sit between the bar and the front handle, right where your left hand rests.
A battery saw follows the same order, with a battery compartment and a switch where the fuel tank and the starter sit on a gas saw. A close-up of the chain shows the cutters on top, the depth gauges in front of each cutter, and the drive links hanging below, the tangs that sit down in the bar groove.
Keep one mental model in mind as you look at any saw. The bar guides and oils, the chain cuts, and the sprocket pulls. Everything else either feeds those three parts or keeps them under control.
The cutting attachment, bar, chain and sprocket
These are the parts that touch the wood, and they are the ones that decide how well the saw cuts.
Guide bar
Also called simply the bar. It is a steel bar with a groove running around its edge. It guides the chain along a straight line, carries oil from the oil hole to the groove so the chain runs lubricated, and its rounded front end, the bar nose, holds the nose sprocket that lets the chain turn the corner. The bar has a groove, two rails on either side of it, an oil hole, and a mounting slot at the tail that slides over the bar studs. Rails wear down and burr, the groove packs with chips, the oil hole clogs, and the nose sprocket wears and gets noisy.
Saw chain
The chain is the part that cuts. Each cutter (the teeth) has a top plate, a side plate and a chrome-plated cutting corner, and they come in left and right pairs so the chain cuts on both sides of the bar. In front of every cutter sits a depth gauge, also called a raker, which sets how deep the cutter bites. The drive links are the tangs underneath that sit in the bar groove and are pushed by the sprocket. Tie straps and rivets hold the whole loop together. A dull cutter, depth gauges filed too low (grabby and kickback-prone) or too high (slow cutting) are the usual problems.
Drive sprocket
The sprocket sits on the clutch drum and pulls the chain around the bar. It comes as a spur sprocket, cut in one piece with the drum, or a rim sprocket, a replaceable ring on a hub. Worn teeth let the chain ride high and chew the drive links, so the sprocket is replaced before the chain is damaged.
Chain pitch and gauge
Pitch is the distance across any three consecutive rivets divided by two. Common pitches are 1/4 inch, 3/8 inch low profile, .325 inch, 3/8 inch and .404 inch. Gauge is the thickness of the drive link where it sits in the bar groove, commonly .043, .050, .058 or .063 inch. Pitch and gauge have to match across the chain, the bar groove and the sprocket, or the chain will not seat and run properly.
Chain tensioner
The tensioner keeps the chain seated in the groove. It is either a screw type, reached from the front or the side of the saw, or a tool-free quick tensioner turned by hand. Check tension cold: the chain should hang about 1/32 inch off the bar at mid-bar, and about 1/8 inch when warm. Lift the chain at mid-bar and three drive links should just clear the rails and snap back when released.
The drive and power parts
Between the engine and the chain sits a small set of parts that transmit power and keep the engine running.
Centrifugal clutch and clutch drum
The clutch shoes sit inside the drum and are held back by springs at idle, so the chain stops. As engine speed rises the shoes swing out, grip the drum and drive the sprocket. That is why a saw idles without the chain moving, and why a chain that creeps at idle points to a worn clutch or an idle set too high.
Sprocket cover and bar nuts
The sprocket cover, also called the side cover or clutch cover, shields the clutch and sprocket and clamps the bar in place. It is held by the bar nuts on the bar studs, and those nuts are worth checking after the first few cuts on a new chain, because a new chain stretches as it seats.
Flywheel, cooling fins and fan housing
The flywheel and its fins, inside the fan housing, pull air across the cylinder and keep the engine cool. A clogged housing is a common cause of overheating.
Spark plug and ignition lead
The plug and its lead ignite the fuel mixture on a gas saw. A fouled plug is one of the first things to check when a saw will not start.
Starter assembly
The recoil starter, with its rope and grip, turns the engine over by hand to start it. The rope and the recoil spring are the parts that fail.
Decompression valve
On larger gas saws, the decompression valve releases cylinder pressure so the starter is easier to pull.
Muffler and spark arrester
The muffler quiets the exhaust, and the spark arrester screen inside it traps sparks. The screen is a required safety part on many public lands, and a clogged screen costs power.
The gas engine support parts you check when your saw starts losing power
A gas saw carries two separate tanks, one for fuel mix and one for bar oil, and a set of parts that feed each of them.
Fuel tank, cap and filter
The fuel tank holds the mix, and the filter on the end of the fuel line inside the tank keeps dirt out of the carburetor. The mix is stated as a ratio: 50:1 is 2.6 fl oz of two-cycle oil per gallon of gas.
Carburetor, air filter and choke
The carburetor mixes fuel with air, and its adjustment screws set the idle and the high-speed mixture. The air filter and its cover keep dust out of the engine, and the choke richens the mix for a cold start. A hard-starting saw or one that loses power often has a dirty air filter.
Primer bulb
The primer, or purge bulb, pushes fuel into the carburetor after the saw has sat for a while, so you are not pulling the starter dry.
Bar oil tank, oil pump and adjustment screw
The oil path runs from the tank through the pump, out the bar oil hole, along the bar groove and onto the chain. The oil-pump adjustment screw sets how much oil reaches the bar. A working oiler leaves oil in the bar oil tank when the fuel tank runs dry, which is the simplest check you can do.
Master control lever
On many saws one lever combines choke, fast idle, run and stop, so starting and shutting down take one thumb.
Handles, controls and the safety group
The safety parts are the ones worth learning first, because they are what stands between you and a kickback injury.
Front and rear handles
The front handle, or handlebar, comes as a half-wrap or a full-wrap, and the rear handle holds the trigger. Both are tied to the powerhead by the anti-vibration mounts.
Throttle trigger and lockout
The trigger opens the throttle, and the throttle lockout must be pressed before the trigger will move. It is a safety interlock, not a cruise control.
On/off switch
The kill switch grounds the ignition on a gas saw and cuts power on an electric or battery saw.
Chain brake and front hand guard
On most saws the front hand guard is also the brake lever. The brake clamps a band around the clutch drum and stops the chain, and it trips either from your hand pushing the guard forward or by inertia in a kickback. It is a kickback safety device, not a parking brake. Check it before every use: rev the saw briefly, push the guard forward, and the chain must stop.
Chain catcher
The chain catcher is a small hook under the bar near the body. If the chain is thrown or breaks, the hook catches it before it reaches your leg.
Bumper spikes
Also called felling dogs or bucking spikes, these metal teeth at the front of the powerhead grip the wood and give you a pivot point for controlled cutting.
Anti-vibration mounts
Springs or rubber blocks sit between the powerhead and the handles and cut down the vibration that reaches your hands.
Rear hand guard and gunning sights
The rear hand guard protects your right hand, and the gunning sights, or felling direction marks, are alignment marks on the body used to aim a fell.
Scabbard and scrench
The scabbard, or bar cover, guards the bar and chain in transport. The scrench is the combination wrench that comes with most gas saws, with a screwdriver on one end and a bar-nut wrench on the other.
The kickback zone
The upper quadrant of the bar nose is the kickback zone. If that corner touches wood while the chain is moving, the saw can kick up and back toward you, which is exactly what the chain brake is there to stop.
Which parts each type of saw has
Every chainsaw shares the same core, and the differences sit in how the power is made and where the controls are placed.
| Part | Gas | Corded electric | Battery | Top-handle mini | Pole saw |
|---|---|---|---|---|---|
| Guide bar, saw chain, drive sprocket | Yes | Yes | Yes | Yes | Yes, at the head |
| Chain tensioner and sprocket cover | Yes | Yes | Yes | Yes | Yes |
| Chain brake, front hand guard, chain catcher | Yes | Yes | Yes | Yes | Yes |
| Throttle trigger and lockout, on/off switch | Yes | Yes | Yes | Yes | Yes, at the handle end |
| Bar oil tank and oiler | Yes | Yes | Yes | Yes | Yes, at the head |
| Anti-vibration mounts | Yes | Yes | Yes | Yes | Yes |
| Fuel tank, carburetor, choke, primer bulb | Yes | No | No | Yes | Gas models only |
| Decompression valve, recoil starter, muffler, spark plug | Yes | No | No | Yes | Gas models only |
| Centrifugal clutch in the usual sense | Yes | No | No | Yes | Gas models only |
| Electric motor, controller, battery compartment or cord | No | Yes | Yes | No | Battery and corded models |
| Shaft or drive tube, gear head, harness hook | No | No | No | No | Yes |
Battery and corded saws
These have an electric motor, a controller and a battery compartment or a cord instead of an engine. They have no fuel tank, carburetor, choke, primer bulb, decompression valve, recoil starter, muffler or spark plug. Everything that touches the wood, and every safety part, is the same as on a gas saw.
Top-handle mini saws
On a top-handle saw the rear handle sits on top of the powerhead. These saws are built for one-handed work in a tree by trained arborists, not as a homeowner felling saw. A small pruning saw can look like a one-handed tool, but it is not one.
Pole saws
A pole saw puts the powerhead at the handle end and adds a shaft or drive tube, often telescopic with locking collars, and a gear head at the cutting end. The bar and chain sit at the head, the oil tank sits at the head too, and a harness support hook takes the weight off your arms.
Parts that wear out first, and the warning sign
Wear shows up as a change in how the saw cuts or sounds before it shows up as a broken part.
| Part | Warning sign | What it means |
|---|---|---|
| Chain cutters | Slow cutting, fine dust instead of chips, a cutter shorter than about 0.16 inch (4 mm) | Sharpen, or replace the chain |
| Depth gauges | Grabby cutting, or slow cutting | Check the setting, typically about .025 inch |
| Drive sprocket | Hooked or worn teeth | Replace it, and a common rule of thumb is a new sprocket every two to three chains |
| Bar rails and nose sprocket | A raised burr, a chain that wanders, a noisy nose | Dress the rails or replace the bar |
| Chain tension | A chain that hangs loose or is tight enough to bind | Re-tension it |
| Air filter | Hard starting, loss of power | Clean or replace it |
| Spark arrester screen | Clogged screen, loss of power | Clean it |
| Chain brake band | The brake no longer stops the chain in the check | Have it serviced |
A 30-second parts check before every use
Run this check with the saw off and the chain brake engaged, then start it for the brake check.
- Chain brake. Rev briefly and push the guard forward. The chain must stop.
- Throttle lockout. The trigger must not move until the lockout is pressed.
- Chain catcher. It must be present and not bent away from the bar.
- Anti-vibration mounts and fasteners. They must be tight and not cracked.
- Spark arrester. On a gas saw, the screen must be present and clean.
Then check the chain tension, the bar oil level, and the bar nuts after the first few cuts on a new chain, because a new chain stretches as it seats.
Every part of a chainsaw either feeds the powerhead, the cutting attachment or the safety group, or protects you from it. Learn the safety parts first, the chain brake, the front hand guard, the chain catcher and the throttle lockout, because they are what you check before every start. Then learn the wear parts, the chain, the sprocket and the bar, because those decide whether the saw cuts well or fights you. The same names apply on a gas, battery, corded, top-handle or pole saw, with the differences listed in the comparison table above.
Frequently asked questions
Most confusion about chainsaw parts comes from the same few names: the teeth are cutters, the spikes are bumper spikes, and the part that turns the chain is the drive sprocket.
What are the main parts of a chainsaw?
Three groups cover the whole saw: the powerhead with the engine or motor and the controls, the cutting attachment that touches the wood, and the safety group that keeps the chain under control. The safety group is the one to learn first.
What is the part that turns the chain called?
It is the drive sprocket, mounted on the clutch drum. The clutch grips the drum as engine speed rises, and the drum turns the sprocket, which pushes the drive links around the bar.
What are the teeth on a chainsaw chain called?
They are the cutters. The left and right cutters are mirror images of each other, so a chain has to be sharpened from both sides to keep the teeth even.
What is the difference between the bar and the chain?
The bar is a steel guide with a groove, and it carries oil to the chain. The chain is the loop of cutters that actually removes wood. A sharp chain on a worn bar still cuts badly, so both matter.
What does the chain brake do, and how do I check it?
It is a kickback safety device, not a parking brake, so it is not meant to hold the chain while you carry the saw or set it down. If the brake ever fails the check, stop using the saw and have the band serviced before the next start.
What does the chain catcher do?
It is a passive part with nothing to adjust, but it is easy to bend or lose in a fall or a drop. Look at it during the pre-use check: if it is bent away from the bar or missing, replace it before cutting, because it only works if it sits where the chain can reach it.
What is a depth gauge and what does it do?
The depth gauge, or raker, is the small hump in front of each cutter. It sets how deep the cutter bites into the wood. Too high and the saw cuts slowly, too low and it grabs and kicks back.
What does the oil pump adjustment screw change, and how do you know the oiler is working?
The oil path runs from the bar oil tank through the oil pump, out the bar oil hole, along the bar groove and onto the chain, and the oil-pump adjustment screw sets how much oil reaches the bar. The simplest check is to run the saw until the fuel tank is dry: a working oiler still leaves oil in the bar oil tank.
What is the clutch for, and why doesn't the chain spin at idle?
The clutch is centrifugal. Its shoes are held back by springs at idle, so the drum and the chain stay still. As engine speed rises the shoes swing out and grip the drum, and the chain starts to move.
What is the decompression valve for?
It releases pressure from the cylinder so the starter rope pulls more easily. It is found on larger gas saws, where the compression would otherwise make starting hard work.
What is the master control lever?
It is a single lever on many gas saws that combines choke, fast idle, run and stop. One thumb sets the saw for a cold start, for running, or for shutting it off.
What is the difference between a front and a side chain tensioner, and how tight should the chain be?
A front tensioner is reached at the front of the saw, a side tensioner at the side of the sprocket cover, and a quick tensioner is turned by hand without tools. Cold, the chain should hang about 1/32 inch off the bar at mid-bar, and about 1/8 inch when warm.
What is the difference between a top-handle and a rear-handle chainsaw?
On a top-handle saw the rear handle sits on top of the powerhead, which lets a trained arborist work one-handed in a tree. A rear-handle saw puts the handle behind the powerhead and is the layout for ground work such as felling and bucking.
Do battery chainsaws have a clutch, carburetor or fuel tank?
No. A battery saw has an electric motor, a controller and a battery compartment instead of an engine, so there is no fuel tank, carburetor, choke, primer bulb, decompression valve, recoil starter, muffler or spark plug. The bar, chain, sprocket, oiler and safety parts are all still there.
What parts does a pole saw have?
The powerhead sits at the handle end, followed by a shaft or drive tube, often telescopic with locking collars, and a gear head at the cutting end. The bar and chain and the oil tank are at the head, and a harness support hook carries the weight.
Which parts wear out first?
The chain cutters and the drive sprocket go first, then the bar rails and nose sprocket. The air filter and the spark arrester screen clog next. The chain brake band is the safety part that needs attention soonest if the brake check ever fails.
What is a scrench?
It is the small combination wrench that comes with most gas saws. One end is a screwdriver for the tensioner and carburetor screws, and the other is a wrench sized for the bar nuts.
What are gunning sights?
They are alignment marks molded into the body of the saw, used to line up a felling cut with the direction you want the tree to fall. They are a guide for aiming, not a measuring tool.
What is the anti-vibration system for?
Springs or rubber blocks separate the handles from the powerhead, so less vibration reaches your hands. That reduces fatigue and the tingling numbness that comes from long sessions with a running saw.
What is a spark arrester and why does it matter?
It is a metal screen in the muffler that traps hot sparks before they leave the saw. It is required on many public lands, and a clogged screen also costs the engine power, so it is worth cleaning.