Short answer: every chainsaw chain is defined by three numbers — pitch (how far apart the rivets are), gauge (how thick the drive links are), and drive-link count (how many links go around the bar). Bar length alone will not order you a chain. A 16" bar can take 55, 56 or 57 drive links depending on the make and the sprocket, so the count has to come off the bar stamp or off a physical count.
Pitch: measure three rivets, divide by two
Pitch is the distance between any three consecutive rivets divided by two. It has to match your drive sprocket and the bar nose sprocket, so it is the one number you can never fudge.
| Pitch | Metric | Typical use |
|---|---|---|
| 1/4" | 6.35 mm | Compact top-handle and carving saws; very fine kerf |
| 3/8" low profile (marked 3/8" LP, 3/8"P or 91-series) | 9.32 mm | Most homeowner saws and electric/battery saws |
| .325" | 8.25 mm | Mid-size farm and ranch saws, 45–55 cc class |
| 3/8" standard | 9.52 mm | Professional 55–90 cc saws, longer bars |
| .404" | 10.26 mm | Large-displacement and harvester saws |
3/8" low profile and 3/8" standard are not interchangeable. They share the nominal pitch figure but use different cutter and drive-link geometry, and low-profile chain runs on a low-profile sprocket. If a chain fits the sprocket but rides high in the groove, you have mixed them.
Gauge: the thickness of the drive-link tang
Gauge is how thick the part of the chain that rides in the bar groove is. Too thin and the chain rattles and derails; too thick and it will not seat at all.
| Gauge (inch) | Metric | Notes |
|---|---|---|
| .043" | 1.1 mm | Lightweight and battery saws; narrow-kerf bars |
| .050" | 1.3 mm | The most common homeowner gauge by a wide margin |
| .058" | 1.5 mm | Mid to heavy-duty bars |
| .063" | 1.6 mm | Professional and long-bar work |
The easy field test: a US quarter is about .058", a US penny about .050" and a US dime about .043". Slide one into a clean bar groove — the coin that fits snugly is your gauge. Clean the groove first; packed sawdust will fool the test.
Drive links: count them, do not guess them
Drive links are the pointed tangs on the underside of the chain that run in the groove. The count is set by the bar length and the bar design, which is why two 18" bars from different makers can call for different chains. Two reliable ways to get the number:
-
Read the bar stamp. Most bars are stamped near the mounting slot with all three numbers, for example
3/8"P 1.3 mm 50or.325 .058 72DL. Wire-brush the paint off if it is faded. - Count by hand. Lay the old chain flat, mark the first drive link with a paint pen, and count around to the mark. Count the tangs, not the cutters — cutters are roughly half the number and are the single most common ordering error.
Rough guide only, to sanity-check a number you have already read or counted: a 14" bar usually runs somewhere in the high 40s to low 50s; a 16" bar in the mid 50s to high 50s; an 18" bar around the mid 60s to low 70s depending on pitch; a 20" bar in the low to high 70s. Use this to catch a typo, never to place an order.
Ordering the right chain, step by step
- Find the bar stamp and write down pitch, gauge and drive links in that order.
- If the stamp is unreadable, measure pitch across three rivets, test the gauge with a coin, and count the drive links on the old chain.
- Note whether you want full chisel (square corner, fastest in clean wood, dulls quickly in dirt), semi-chisel (rounded corner, holds an edge in dirty or frozen wood), or a low-kickback safety chain.
- Check the drive sprocket while the chain is off. A sprocket with visible wear grooves will chew a new chain in a season — replace it at every second or third chain.
- Check bar-groove wear at the same time. If the chain leans sideways when you pull it up at the mid-bar, the rails are worn.
Quick answers
Can I put a .050" chain on a .058" bar? Physically yes, safely no. The chain will wobble in the groove, cut crooked and wear the rails.
Is a longer bar always better? No. Bar length has to stay within the saw powerhead rating; over-barring bogs the engine and increases kickback risk.
Why do the same saws use different chains across model years? Makers change bar suppliers and sprocket types between production runs. Always order off the bar in front of you, not off the machine name.
How many chains should I keep? Two or three per bar, rotated. Swapping a dull chain in the field beats field-sharpening, and a rotation lets you sharpen everything in one session.
Do aftermarket chains fit OEM bars? Yes, when pitch, gauge and drive-link count all match. Those three numbers are an open industry standard.
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Full selector: chainsaw chain size and gauge chart.