What Is a 50cm Chainsaw Guide Bar? (Gauge Specs)
A 50 cm chainsaw guide bar is a bar with a nominal length of about 19.7 inches, often sold as a 20-inch bar. That measurement is not the bar’s gauge. To fit safely, the bar, chain, and saw must match in mount, pitch, groove gauge, and drive-link count, and the bar length must be approved for the saw.
If you found “50 cm” in a product listing or manual, it can be easy to mistake it for a chain specification. It is not. The number describes the bar’s nominal length, while other measurements decide whether a particular chain will fit and run correctly.
I explain those measurements as separate checks because length alone cannot confirm compatibility. A mismatch may stop the chain from fitting, damage parts, or raise the risk of a chain coming off. Use the saw and chain maker’s fitment information rather than guessing.
50 cm Bar Fitment, Gauge, and Safety Preparation
A 50 cm bar is roughly 19.7 inches long and is commonly sold as a 20-inch bar. Its usable cutting length is shorter than its nominal length. To check fit, compare the saw’s approved bar options with the bar mount, chain pitch, groove gauge, and required drive-link count.
What the bar and chain measurements mean
The bar mount is the shape and hole pattern where the bar attaches to the saw. It must match the saw. The gauge is the width of the groove in the bar; the chain’s drive links, the small tabs that sit inside that groove, must fit it.
The pitch describes the spacing of the chain’s cutting links and rivets. It must match the bar’s nose sprocket and the chain. The drive-link count is the number of tabs that travel inside the bar groove. It depends on the bar and saw setup, so length, pitch, and gauge alone do not tell you the correct count.
| Specification | What it describes | Common check |
|---|---|---|
| Bar length | Nominal length of the bar | 50 cm is about 19.7 in, often called 20 in |
| Gauge | Width of the bar groove and chain drive links | .050 in (1.3 mm) and .058 in (1.5 mm) are common; they are not interchangeable |
| Pitch | Chain and sprocket spacing | .325 in and 3/8 in are common options; match the saw, bar, and chain |
| Drive links | Number of chain tabs that run in the bar groove | Read the bar marking or the saw or chain fitment chart |
| Mount | Bar’s attachment pattern | Match the exact saw model or approved replacement type |
A 3/8-inch low-profile chain is a distinct chain system. Do not assume it fits a 20-inch bar just because the length sounds right. Check the maker’s fitment chart for the exact saw, bar, and chain combination.
How I check whether a 50 cm bar will fit
I start with the chainsaw model and its operator’s manual, not the bar’s length. The manual or maker’s parts chart should identify approved bar lengths and may list compatible mounts, pitches, and chain options. A longer bar can place more demand on a saw, but there is no dependable universal rule that links engine size to bar length.
Check the markings on the current bar and chain, then compare them with the replacement details. If a marking is worn or unclear, use the saw maker’s parts information or ask a qualified dealer to confirm the fit. Do not choose a chain by appearance.
Practical fitment scenarios
These are examples of how to check a setup, not claims about a particular saw model:
- The replacement bar is 50 cm, but its gauge is .058 inch. If the chain is .050 inch, the groove and drive links do not match. Find a compatible chain and verify the pitch, link count, mount, and saw approval before use.
- The bar and chain both say .050 inch, but the pitch differs. They still do not form a compatible setup. Confirm that the chain pitch matches the bar sprocket and the saw’s required chain system.
- The length and pitch match, but the drive-link count is unknown. Do not estimate it from bar length. Check the bar marking or the maker’s fitment chart.
Prepare the saw before use
Before fitting or running a bar, wear suitable protective equipment: a helmet with eye and face protection, hearing protection, chainsaw chaps, gloves, and protective boots. Inspect the chain brake, throttle lockout, chain catcher, chain, bar rails, and oiling system. Follow the saw’s manual and the safety rules that apply to your work, including relevant ANSI Z133 and OSHA requirements where applicable.
Check the work area before starting. Look for people nearby, overhead hazards, unstable footing, targets, and a clear escape route when the task calls for one. Felling or storm-damage work needs suitable planning and skill; bar length does not make that work safe by itself.
Field Cutting: Matching the Bar to the Saw and Work
A 50 cm bar is suitable only when the saw maker approves that length for the specific saw and the chain matches the bar. The work matters too: wood type, diameter, and how long the saw will run can affect the load. Do not use bar length alone to judge capacity.
Start and verify the setup
Follow the manual’s cold- or warm-start steps, and start the saw on stable ground. Before cutting, confirm that the chain brake works, the chain stays still at idle, the chain tension is correct, and oil reaches the chain and bar. Use the maker’s check for oil delivery; do not guess at an oil-flow rate.
Fuel mix, idle speed, maximum engine speed, chain tension, and bar-oil requirements vary by model. Use the operator’s manual for each one. A bar’s 50 cm length does not tell you the correct fuel ratio, RPM, or oil specification.
Hold the saw with both hands and keep a stable stance. Let a sharp, correctly tensioned chain cut without forcing it. Do not cut above shoulder height, and keep the upper quadrant of the bar nose clear of wood and other objects. Contact there can cause kickback, a rapid rotation of the saw toward the operator. A working chain brake is important, but it does not replace safe technique.
Choose the bar for the actual task
A 50 cm bar may let a trained operator reach across a wider cut than a shorter bar, but it does not make every cut appropriate for the saw. Dense hardwood, large-diameter wood, or sustained commercial work can place greater demands on the equipment. Check the saw maker’s approved combinations and work within your training.
| Situation | What to verify before cutting |
|---|---|
| Replacing a worn bar with another 50 cm bar | Same approved mount and compatible pitch, gauge, and chain length |
| Cutting larger or denser wood | The saw maker approves the bar for the saw and task; the chain is sharp and correctly set |
| Running a low-profile chain | The saw, bar, and chain maker specify that exact system |
| Doing prolonged work | The saw is approved for the bar and use; follow the manual’s operating and service guidance |
A useful decision is not simply “Will this bar reach the wood?” It is “Is this bar approved for my saw, does the complete chain system match, and can I make the cut safely with my skill and setup?”
Chain Sharpening, Tension, and Bar Maintenance
The chain must fit the bar groove and sprocket, stay at the correct tension, and be sharpened to the chain maker’s specifications. Routine checks help catch wear and poor oiling before they affect cutting. The exact settings vary by chain, bar, and saw, so use their instructions rather than copying a setting from another setup.
Check tension and sharpen to specification
Use the manual’s chain-tension procedure. A chain that is too loose can come off the bar; one that is too tight can add strain and wear. Check tension as directed, especially when the chain is new or has changed temperature during use. Stop the engine and follow the manual before adjusting it.
Sharpen the cutters with the correct file size and filing guide for that chain. The raker, also called the depth gauge, controls how much wood a cutter takes in each pass. A .025-inch (0.63 mm) setting is common on some chains, but it is not a universal setting. Use the chain maker’s specification and the proper depth-gauge tool.
Inspect the bar and oiling system
Stop the engine before servicing. Check the bar rails for uneven wear or damage, and clear dirt from the groove and oil hole. Confirm that the chain and bar receive oil using the method in the manual. Poor oil delivery can increase friction and wear, so do not keep cutting if the system appears not to be working.
If the bar has reversible markings or instructions, follow the bar maker’s guidance on turning it. Replace or service worn parts as directed. Do not try to correct a pitch, gauge, or mount mismatch by adjusting the chain or bar.
Shutdown, Cleaning, and Seasonal Storage
After cutting, engage the chain brake and stop the engine before setting the saw down or starting service. Let hot parts cool, then clean and inspect the bar, chain, and oiling areas. For storage, follow the manual’s instructions for fuel, chain care, and protective covers; storage steps differ by model.
When cleaning, clear debris from the bar groove and oil hole, inspect the rails, and check chain condition and tension. Refuel only as directed by the operator’s manual, away from ignition sources and with the engine stopped and cool as specified. Use the manual for fuel handling and storage; do not infer a fuel procedure from bar size.
The key point is that 50 cm tells you the bar’s nominal length, not whether the bar and chain fit your saw. Confirm every compatibility detail before use, and stop if you cannot verify the setup.
FAQ
Is a 50 cm chainsaw bar the same as a 20-inch bar?
It is close. Fifty centimetres is about 19.7 inches, and bars of this nominal length are commonly sold as 20-inch bars.
Does 50 cm describe the bar gauge?
No. It describes nominal bar length. Gauge is the width of the bar groove and must match the chain’s drive-link thickness.
What gauge is a 50 cm chainsaw bar?
There is no single gauge for all 50 cm bars. Common gauges include .050 inch (1.3 mm) and .058 inch (1.5 mm). Check the bar marking and chain specification.
Can I use a .050-inch chain on a .058-inch bar?
No. The chain’s drive-link thickness must match the bar groove. Those gauges are not interchangeable.
Is a 20-inch bar always compatible with a 3/8-inch chain?
No. The chain pitch must match the bar sprocket and the saw’s approved chain system. Check the fitment information for your model.
How many drive links does a 50 cm bar need?
There is no universal count. Use the number on the bar or the saw, bar, or chain maker’s fitment chart.
Can I put a 50 cm bar on any chainsaw?
No. The mount, approved bar length, chain pitch, gauge, and drive-link count must all match the saw and its bar.
Is a 50 cm bar’s usable cutting length exactly 50 cm?
No. Usable cutting length is less than the nominal bar length. The exact amount depends on the bar and saw setup.
Can I use the bar length to choose the fuel mix or chain tension?
No. Fuel mix, tension, oiling, and engine-speed settings are model- or chain-specific. Follow the operator’s manual and chain maker’s instructions.
What is the main kickback risk with a 50 cm bar?
Kickback can occur if the upper quadrant near the bar nose contacts wood or another object. Keep that area clear, maintain a firm two-handed grip, and use a working chain brake without relying on it as a substitute for safe technique.
(This article was written by one of our staff writers, Evan Bradley. Visit our Meet the Team page.)
