Stihl MS 251 C Chainsaw Chain (Fitment Guide)

For an MS 251 C, match the chain to the bar and drive sprocket, not just the saw model. Many North American setups use 3/8-inch P pitch and .050-inch gauge, with 55 drive links for a 16-inch bar or 62 for an 18-inch bar. Check the bar stamp and chain code before buying; packages can vary.

A chain that looks close may still be wrong. Pitch must match the sprocket and bar nose, gauge must fit the bar groove, and the drive-link count must suit the bar. Get all three right before installing a replacement.

The MS 251 C has a 45.6 cm³ two-stroke engine. Its chain fitment can vary with market and bar package, so treat common specifications as a starting point, not a final answer. I check the installed bar markings first, then confirm the chain and sprocket. That simple order prevents a common mistake: buying by model name alone.

Match the chain to the installed bar

The chain’s pitch, gauge, and drive-link count are separate measurements. Each must match the parts already on the saw. Common North American MS 251 C combinations include 3/8-inch P pitch, .050-inch gauge, and either 55 or 62 drive links, but the bar stamp and chain code decide the fit.

These combinations are useful clues, not a guarantee that every MS 251 C has that bar. Look for the pitch, gauge, and drive-link count stamped on the guide bar. If the markings are worn or unclear, identify the chain by its code or count its drive links. Drive links are the small teeth along the bottom of the chain that sit in the bar groove.

Pitch describes the spacing between chain rivets; gauge is the thickness of the drive links. The chain pitch must also match the drive sprocket and bar nose. A mismatch can cause poor running, damage, or a chain that does not seat correctly. Do not file, force, or “make fit” an incompatible chain.

Illustrative fitment checks: If the bar is stamped for 3/8-inch P and .050-inch gauge and has 55 drive links, compare those details with the replacement chain label before purchase. If an 18-inch bar is installed, do not assume the 16-inch chain’s link count will work. Recheck the bar stamp and count the links if needed.

For any uncertain marking, take the old chain or a clear photo of its code and bar stamp to a parts counter. Confirm the sprocket pitch as well, especially if the sprocket or bar may have been changed. Next step: record the bar’s pitch, gauge, and drive-link count before ordering.

Equipment Setup, Chain Fitment & Safety Preparation

Fitment is only one part of readiness. Before removing or installing a chain, make the saw safe and check the bar, sprocket, and chain for wear or damage. Then set the chain direction and tension as the applicable STIHL manual directs; correct fit does not make a damaged part safe to use.

Wear chainsaw-protective legwear, gloves, boots, helmet, eye or face protection, and hearing protection. Clear the work area, identify escape routes, and look for overhead hazards. Check the chain brake, throttle lockout, catcher, handles, and chain condition before starting. Follow applicable safety rules, including relevant ANSI Z133 or OSHA requirements.

To fit a compatible chain:

• Shut the saw off and let hot parts cool. Engage the chain brake and wear gloves when handling the cutters.
• Remove the sprocket cover as the manual describes. Inspect the bar rails, bar nose, drive sprocket, and chain for damage or unusual wear.
• Place the chain around the sprocket and bar. At the top of the bar, the cutter edges must face forward, toward the bar nose.
• Seat the drive links in the bar groove. Refit the cover and adjust tension using the saw’s specified procedure.
• Tighten the bar nuts as directed. Check that the chain is seated and can move by hand with gloves on, without excessive slack. Use the manual’s tension instructions rather than guessing.

A chain that is too loose can come off; one that is too tight can add strain and wear. Recheck tension after the first cuts and after the chain cools, since chain tension changes during use. If the adjuster reaches its limit or the chain will not seat, stop and recheck the parts instead of forcing them.

Before starting, fill the chain-oil tank with suitable bar-and-chain oil and check that the oiling system works as the manual describes. There is no single safe oil-flow rate or viscosity for every condition. Use oil suited to the ambient temperature and verify lubrication at the bar tip. Next step: confirm fit, tension, oil, and safety controls before starting.

Field Cutting and Landscaping Operation

The MS 251 C’s 45.6 cm³ engine is intended for compatible short-to-medium bars and routine cutting tasks such as firewood and tree care. Choose bar length for the work and your control of the saw, not as a rating of wood hardness. Large or hard timber raises the load, so use a sharp chain and sound technique.

Start on stable ground with the chain brake engaged, following the model-specific manual. Never drop-start the saw. Release the brake only when ready to cut, and keep two hands on the saw with a stable stance. Plan each cut around the wood’s support, compression, and tension; if the wood shifts or binds, stop and reassess.

Keep the bar nose clear of branches and other objects. Contact with the upper part of the bar nose can cause kickback, a rapid upward and backward movement of the saw. A working chain brake and low-kickback equipment help reduce risk, but neither replaces safe technique. Avoid cutting above shoulder height.

If the chain stops cutting cleanly, do not push harder. A dull chain can burn wood and make the saw work harder. Stop, shut down, and inspect or sharpen the chain before continuing. A loose chain, poor oiling, or a chain that does not match the bar also calls for a stop, not a test cut. Next step: correct the cause before returning to the cut.

Maintenance, Chain Sharpening & Engine Checks

A sharp, correctly matched chain cuts with less forcing than a dull one. The right file size, filing angle, and depth-gauge setting depend on the exact chain code, so use the chain-specific STIHL chart or manual. Do not apply one file size or raker setting to every chain fitted to an MS 251 C.

Find the chain code on the chain, package, or product information. Then use the matching sharpening instructions for file diameter, filing angle, and depth-gauge setting. Some common 3/8-inch P chain types use a 5/32-inch (4.0 mm) file and a 30-degree filing angle, but do not assume those values apply to an unidentified chain. If the chain code does not match, stop and check the correct chart.

Keep each cutter’s top plate and side plate shape consistent as you sharpen. Use a file guide if it helps you hold the specified angle. Check the depth gauges only as the chain maker directs. A depth gauge, sometimes called a raker, controls how much wood a cutter can take; lowering it too far can make cutting more aggressive. Do not use a universal clearance value.

For fuel, the engine is a two-stroke design. Use fresh unleaded gasoline mixed with quality air-cooled two-stroke oil at 50:1, unless the applicable STIHL manual or oil-maker instructions require otherwise. That equals 20 mL of oil for each 1 L of gasoline. Measure accurately, mix in an approved fuel container, and never run straight gasoline.

Use the model- and serial-specific manual for idle speed, maximum engine speed, chain-brake checks, and service limits. Those values should not be guessed or transferred from another saw. Next step: identify the chain code before sharpening and follow the correct manual for engine service.

Shutdown, Storage & Seasonal Care

Good shutdown and storage habits help protect the chain, bar, and saw between jobs. Stop cutting, engage the brake, and shut down as the manual directs. Let the saw cool before cleaning or handling the chain, then inspect it before storage so damage or a fitment problem is not carried into the next use.

After the saw is cool, wear gloves and check chain tension. Clean debris from the air-intake area, bar groove, oil holes, and sprocket cover. Look for damaged cutters, a worn bar groove, or signs that the chain has not been lubricated. If you find damage or are unsure whether a part is within its service limit, use the model-specific manual or ask a qualified service shop.

Store the saw according to the manual, with the chain protected and the fuel handled as directed for the storage period. Before the next outing, repeat the basic checks: chain fit, tension, chain brake, fuel mix, and bar oil. Next step: record the chain code and bar markings so replacements and sharpening supplies are easy to confirm.

Frequently asked questions

What chain fits a Stihl MS 251 C?
Many North American setups use 3/8-inch P pitch and .050-inch gauge. Confirm the installed bar stamp, sprocket pitch, and required drive-link count before buying.

How many drive links does the MS 251 C chain need?
Common examples are 55 drive links for a 16-inch bar and 62 for an 18-inch bar. Check your own bar; fitment can vary.

Can I choose a chain by bar length alone?
No. Bar length does not confirm pitch, gauge, or drive-link count. Match all three, and confirm pitch against the sprocket and bar nose.

What file size should I use?
Use the file diameter specified for the exact chain code. Some common 3/8-inch P chain types use a 5/32-inch file, but verify before sharpening.

What filing angle should I use?
Follow the chain-specific sharpening chart. A 30-degree angle applies to some chain types, not necessarily every chain that fits this saw.

What fuel mix does the MS 251 C use?
Use a 50:1 gasoline-to-two-stroke-oil mix, following the applicable STIHL manual and oil-maker instructions. That is 20 mL of oil per 1 L of gasoline.

Can I run a chain that feels slightly loose?
No. Stop and set the tension as the manual directs. Do not cut with a loose chain.

How do I know the chain is getting oil?
Use the manual’s check procedure and confirm lubrication at the bar tip. If oiling seems poor, stop and inspect the oil supply and system before cutting.

(This article was written by one of our staff writers, David Hensley. Visit our Meet the Team page.)