Chainsaw Chain Components Explained

A saw chain is closer to a leaf chain than to a roller chain: flat steel links, riveted, with no rollers anywhere. It is an endless loop, and its length is defined by the number of drive links, not by the bar length in inches. The links repeat in a three-link assembly of drive link, tie strap and cutter around the loop.

Cutter (cutting tooth)

The cutter is the only part that cuts. It has a top plate and a side plate that meet at a sharp cutting corner, and cutters alternate left-hand and right-hand around the loop. It works on the planer principle: the top plate lifts a chip off the bottom of the kerf while the side plate severs the wood fibers in the kerf wall. The cutting corner is the first part to dull.

Drive link

The drive link is the fin, or tang, on the inside of the loop. It rides in the guide bar groove and is engaged by the drive sprocket, which is how engine or motor power reaches the chain. It also scrapes debris out of the bar groove as it travels and carries oil around the loop to lubricate the bar and chain. The drive link is where the chain's gauge is measured, and the number stamped on it identifies the chain.

Tie strap

A tie strap is a plain side link with no cutter and no tang. It connects cutters to drive links and holds the loop together. A tie strap with rivets already pressed into it is a preset tie strap; the matching half with bare rivet holes is a plain tie strap. The pair is what lets a loop be joined or repaired.

Rivet

The rivet is the pin that joins the links and acts as the pivot. The chain's pitch is derived from rivet spacing, which is why the rivet is the reference point for the whole identification system.

The cutter looks like one small piece of steel and is really a set of working surfaces, each with its own job.

• Top plate: the upper cutting surface. It lifts the chip and sets the kerf width.
• Side plate: the vertical cutting edge. It does most of the severing of the long wood fibers in the kerf wall.
• Cutting corner: where top plate and side plate meet. It starts the cut and dulls first.
• Depth gauge (raker): the tab in front of each cutter. It limits how far the cutter can tilt into the wood, which sets chip thickness.
• Gullet: the recess between cutter and depth gauge that carries chips out of the cut.
• Witness mark: the line on the cutter that marks the sharpening limit. Once the cutter is filed back to it, the chain is worn out.
• Heel and toe: the rear and front of the cutter body, reference points rather than working edges.

The depth gauge is the component that governs how the saw behaves in the wood. Set too high, the saw cuts slowly and makes fine dust. Set too low, the saw grabs, chatters, bogs and the kickback risk rises. As a cutter is sharpened back it gets shorter, so the depth gauge has to come down with it to keep the setting.

Cutters alternate left, right, left, right around the loop so the chain cuts a kerf of even width and tracks straight. Each side removes its half of the kerf. If the left and right cutters are not sharpened to the same length and the same depth-gauge height, the chain steers, which is why a chain that cuts crooked or pulls to one side usually has uneven cutters rather than a bent bar.

Some chains add bumper drive links, bumper tie straps and ramped depth gauges: extra humps that limit how much the cutter can bite as it rounds the bar nose. These are the low-kickback features.

Kickback happens when the upper quadrant of the bar nose contacts something or the kerf pinches, and it throws the bar up and back toward the operator. Chain geometry is the first line of defense, alongside the chain brake, the front hand guard and a reduced-kickback bar. Low-kickback chain reduces but does not eliminate kickback.

The US standard is ANSI/OPEI B175.1. Saws under 3.8 cu in (62 cc) must meet its low-kickback provisions; saws of 3.8 cu in and larger may or may not. Low-kickback chain carries a green label (older stock: blue), professional non-low-kickback chain a yellow label. The trade-off is real: low-kickback chain cuts less aggressively, and boring cuts become slow or impractical.

The sequence of links around the loop is called the cutter sequence, and there are three arrangements.

• Full complement (standard): cutter, tie strap, cutter, tie strap. Maximum teeth, the smoothest cut, the slowest, and the most load on the powerhead. Virtually every homeowner saw runs it.
• Semi-skip: cutter, two tie straps, cutter, one tie strap. A compromise between the two.
• Full skip: cutter, two tie straps, cutter, two tie straps. About a third fewer teeth, used on long bars, big wood or an underpowered powerhead. It clears chips faster, needs less sharpening and cuts rougher.

The shape of the cutter decides how fast the chain cuts, how long it holds an edge and how hard it is to bring back.

• Chipper: the most rounded profile, easiest to file, tolerates dirt, cuts smoothly and is the slowest.
• Semi-chisel: a rounded leading edge. Slower than full chisel but holds an edge in dirty wood and is easy to file, which makes it the usual all-round choice for firewood and general homeowner work.
• Full chisel: a square corner and a flat top. The fastest profile, dulls fast in dirt and is harder to file.
• Square-ground chisel: the most aggressive, and it needs a grinder or a specialist to sharpen.
• Low profile: a shorter cutter and a thinner chassis that need less power, found on smaller saws and standard on homeowner and mini saws.
• Carbide-tipped: long life in dirty wood, machine-sharpened only.
• Ripping: semi-chisel ground for cutting with the grain.

Pitch, gauge and drive-link count identify a chain, and each one has to agree with the bar and the drive sprocket.

• Pitch: the distance between any three consecutive rivets, divided by two. Common values are 1/4 in, 3/8 in low profile, .325 in, 3/8 in and .404 in. Pitch must match the drive sprocket and the bar nose sprocket.
• Gauge: the thickness of the drive link where it sits in the bar groove. Common values are .043 in, .050 in, .058 in and .063 in. Gauge must match the bar groove exactly.
• Number of drive links: this defines the loop length.

Read the number stamped on the drive link rather than trying to measure a worn chain, and check the stamp on the bar. Chain, bar and sprocket all have to agree.

One-hand top-handle mini chainsaws and pole saws run the same four components, scaled down. The chain is typically 1/4 in low-profile pitch with a .043 in gauge, and the drive-link count is what changes with bar length: a 6-inch bar commonly runs in the mid-30s of drive links and an 8-inch bar in the mid-to-high 40s. The count varies between saws even at the same bar length, so count the drive links on the old chain rather than assuming.

The components are visibly smaller at this scale: shorter cutters, thinner tie straps, smaller rivets, and a depth gauge that is a smaller tab and easy to overlook when you check the chain.

A symptom on the saw usually points at one component, and the list below matches the two.

• Cuts crooked or pulls to one side: left and right cutters unevenly sharpened, or uneven depth gauges.
• Saw bogs, jumps and chatters: depth gauges filed too low.
• Fine dust instead of chips, and you have to push: dull cutters.
• Chain jumps off the bar: tension, or worn drive-link tangs or a worn sprocket.
• Chain stretches quickly: normal break-in on a new chain, or a worn sprocket. Run a new chain a couple of minutes, then re-tension it.
• Chain runs hot and the bar wears: the drive link's oil-carrying job is compromised, or the bar groove is clogged with debris.

Check chain tension cold, with a small gap between chain and bar about the width of a dime as the usual guide, and check the drive sprocket whenever a chain is changed, because a hooked sprocket will ruin a new chain.