What cars use SAE vs metric?
Most modern cars use metric fasteners, while SAE (inch-based) sizes persist mainly on older U.S. models and certain specialty applications. This distinction matters for repairs, parts compatibility, and the right toolbox setup.
Overview: SAE and metric in the car industry
SAE refers to inch-based threading (for example 1/4"-20 or 5/16"-18), while metric uses millimeter-based threading (such as M6x1, M12x1.5). Over decades, global automakers moved toward ISO metric sizing for most components, making metric fasteners the standard on nearly all contemporary vehicles. SAE sizes are now mostly found on older American cars, certain restoration projects, and a few aftermarket or period-correct fittings.
Before you reach for tools, it helps to know where each system is likely to show up. The following sections offer practical guidance for identifying which cars use SAE versus metric hardware, and how to work safely when you encounter mixed systems.
Examples of vehicles and contexts where SAE may still appear:
- Classic American cars built before the mid-1980s
- Some heavy-duty trucks and specialty applications in North America
- Certain aftermarket parts and restorations aiming for period-correct hardware
- Non-structural or legacy components in older builds or hobby projects
In practice, SAE hardware shows up primarily in legacy or hobby contexts, while metric sizing dominates modern production lines and warranties.
Where metric is standard today
The vast majority of new vehicles worldwide rely on metric fasteners for engine, transmission, brakes, suspension, and body hardware. Wheel studs and lug nuts are typically metric as well, with common passenger-car sizes including M12x1.5 and M14x1.5. This metric standard is especially prevalent in European, Japanese, Korean, and most American models produced since the 1990s and 2000s.
Examples of where metric is standard today:
- Nearly all modern passenger cars and light trucks worldwide
- Most European, Japanese, Korean, and newer American models
- Wheel studs and lug nuts in metric sizes (commonly M12x1.5, M14x1.5, etc.)
- Engine and transmission fasteners, brake components, and suspension hardware
In short, metric is the norm for new vehicles and most service manuals, with rare exceptions on vintage or specialized models.
How to tell whether a fastener is SAE or metric
Identifying the correct system starts with measurement and reference. Use a caliper to measure diameter and a thread gauge to count threads per unit length, then compare to standard SAE and metric charts. When in doubt, consult the vehicle’s service manual or OEM specifications.
Here are steps you can follow:
- Measure the bolt or stud diameter with a caliper to determine approximate size (in millimeters) or inches.
- Determine the thread pitch with a thread gauge or by counting threads per millimeter/inch.
- Compare the measurements to common SAE (e.g., 1/4", 5/16", 3/8" with 20, 18, 24 pitch) and metric (e.g., M6x1, M8x1.25, M12x1.5) standards.
- Check the vehicle’s manual or OEM parts catalog to confirm the exact specification for that component.
Conclusion: Using the correct size and pitch is critical to avoid cross-threading and ensure proper fastener strength. If a replacement part exists in both SAE and metric, always match the manufacturer’s specification.
Be careful when mixing systems
Mixing systems or using the wrong pitch can lead to cross-threading, inadequate clamping force, or component failure. For critical parts such as wheel hubs, brake connections, and main engine fasteners, always use the exact size and pitch specified by the manufacturer. When working on mixed-era vehicles, keep both SAE and metric fasteners on hand and verify each fastener against the OEM specification.
Summary
In the current automotive landscape, metric fasteners are the standard for almost all modern vehicles, while SAE/inch-based hardware persists mainly in older U.S. cars and certain specialty or restoration projects. To work safely and correctly, identify the exact size and pitch from the vehicle’s documentation, use the appropriate tools, and avoid substituting sizes unless the manufacturer explicitly allows it. A quick check of the manual and a reliable parts catalog will save time and prevent damage on repairs and restorations.
Do Japanese cars use SAE or metric?
TEKTON Socket Set, Inch/Metric
A: Japanese cars use METRIC.
Do cars use SAE or metric?
For modern cars, metric is the standard, and you'll use it for the vast majority of work. While SAE (Society of Automotive Engineers) tools, which use inches, are useful for older or some American-made vehicles, they are becoming less necessary.
Metric
- Modern cars: Almost all new cars, regardless of origin, are built using metric fasteners (millimeters).
- Global standard: Metric is the global standard and is used on most vehicles from Japan, Europe, and increasingly, the US.
- Benefit: If you buy one set, a metric set is the most practical choice for general automotive work today.
SAE
- Older vehicles: SAE (inches) is primarily needed for older American-made cars and some specific parts.
- Mixed systems: Some cars, especially older ones, may have a mix of SAE and metric fasteners.
- Damage risk: Using an SAE tool on a metric bolt, or vice versa, can damage the fastener by stripping or rounding it off.
Recommendation
- For most modern cars, a metric socket set is sufficient: and is the best starting point for any toolkit.
- If you work on older vehicles, or want to be prepared for all situations, you will need both: metric and SAE tools.
- Always use the correct tool for the fastener to avoid damage.
Is Tesla metric or SAE?
Tesla vehicles are predominantly metric, although some minor SAE hardware may be encountered, especially in older designs. Modern US-built cars, including Teslas, have largely transitioned to a metric system for their fasteners and components.
- Metric Dominance: The overwhelming majority of Tesla components and fasteners, such as lug nuts and internal bolts, are metric.
- Minor SAE Hardware: While rare, you may still find some SAE (American Standard) hardware on the vehicle. It's a good idea to have a basic SAE set for these occasions, though most repairs will use metric tools.
- Transition from SAE: The US automotive industry began phasing out SAE hardware decades ago, with most cars designed entirely with metric hardware since around 1980.
Do we use metric or SAE in the USA?
In fact, the U.S. system is considered a hybrid system, in which both U.S. customary and metric system measurements are used routinely. In the grocery store, we commonly use a mix of milliliters, liters, grams, kilograms, quarts, pints, and pounds.
