What Size Nut On Battery Terminal?

The battery is the heart of your vehicle’s electrical system, providing power to start the engine and run accessories when the alternator is not operating. To deliver this power, battery terminals must be tightly fastened using the proper nut size for your specific battery and vehicle. Using an improperly sized nut can lead to a loose connection resulting in electrical issues, or even damage the battery post.

What Size Nut On Battery Terminal? When replacing your car’s battery or servicing the terminals, it’s essential to identify and utilize the correct nut size on the battery terminal. This article will act as a helpful guide, outlining the common nut sizes used, recommendations for selecting the right fit, best practices for installing and tightening battery terminal nuts, and maintenance tips to keep your electrical connections optimized.

Common Nut Sizes Used On Battery Terminals

The most frequently used nut sizes for battery terminal posts fall into two main categories: metric and SAE (Society of Automotive Engineers) sizes. Within each category, there are a few specific sizes that are widely used by battery and auto manufacturers.

Common Nut Sizes Used On Battery Terminals
Common Nut Sizes Used On Battery Terminals

Metric Sizes

Many modern batteries use metric sized terminal nuts and posts. Some of the common metric battery terminal nut thread sizes include:

  1. M5 – This is a 5 mm diameter nut with a coarse pitch thread. It fits on a 5 mm diameter battery post.
  2. M6 – A 6mm diameter nut that fits on a 6mm post. This is one of the most widely used metric battery terminal nut sizes.
  3. M8 – An 8mm diameter nut for an 8mm post. Often used on larger higher capacity batteries.
  4. M10 – A 10mm diameter nut that fits a 10mm terminal post. Also frequently found on heavy duty and large capacity batteries.

SAE Sizes

Many traditional American and domestic vehicle batteries use SAE sized terminal nuts and posts. Some of the most prevalent SAE battery terminal nut thread sizes are:

  1. 1/4″-20 – A 1/4 inch diameter, 20 threads per inch nut. This fits smaller 1/4″ terminal posts.
  2. 5/16″-18 – The most common SAE battery terminal nut size, with 5/16 inch diameter and 18 threads per inch.
  3. 3/8″-16 – A larger 3/8 inch diameter nut with 16 threads per inch. Used on heavy duty battery applications.
  4. 7/16″-14 – A 7/16 inch diameter nut with 14 threads per inch. Only occasionally used for large capacity batteries.

Choosing The Right Nut Size

Selecting the proper nut size for your battery’s terminals requires verifying the thread diameter and pitch of your terminal posts. Here are some tips on determining the right nut size:

  1. Consult your battery specifications – The battery documentation or label should indicate the thread size of the terminal posts. This is the best way to identify the correct nut size needed.
  2. Check your owner’s manual – Some vehicle manuals provide battery terminal nut size specifications you can reference.
  3. Measure the terminal diameter – Use a caliper or measuring tape to determine the outer diameter of the post which corresponds to the nut’s inner diameter.
  4. Count threads per inch – Use a thread pitch gauge or carefully count the number of threads over one linear inch on the battery post to determine the thread pitch.
  5. Refer to common sizes – If you can’t find specifications, the common metric and SAE sizes listed above can provide guidance on the appropriate nut size.
  6. Compared to the old battery – In many cases, the replacement battery will use the same terminal nut sizes as the old battery.

Choosing the right size ensures proper clamping force is applied to the terminal when tightened. An ill-fitting nut risks inadequate electrical contact and thermal transfer.

Proper Installation Of Battery Terminal Nuts

Once you’ve identified the correct nut size for your battery terminals, proper installation is key to maximizing performance. Follow these best practices when installing battery terminal nuts:

Proper Installation Of Battery Terminal Nuts
Proper Installation Of Battery Terminal Nuts

Clean Terminals and Nuts

  1. Use a wire brush to clean any corrosion or build-up off the battery posts and terminal nuts prior to installation. This allows for optimal electrical contact.

Apply Protective Compound

  1. Coat the battery posts with a thin layer of dielectric or anti-corrosion grease or spray. This prevents moisture and corrosion issues.

Hand Tighten Nut First

  1. Initially hand tighten the nut fully onto the battery terminal by hand without tools. This will allow you to then gauge the proper torque needed.

Torque Nut Properly

  1. Using an inch-pound torque wrench, tighten the nut to the battery or vehicle manufacturer’s specifications. Typical torque values range from 60-120 inch-lbs.

Avoid Overtightening

  1. Do not overtighten the terminal nut, as this can cause damage to the battery post over time, leading to failure.

Proper torque ensures a tightened connection without risking damage. Always refer to your battery’s documentation for explicit torque instructions.

Maintenance Tips For Battery Terminal Nuts

To keep your battery terminal connections optimized, follow these maintenance practices:

  1. Periodically inspect nuts – Check for looseness or corrosion buildup every few months and retighten or clean as needed.
  2. Replace nuts if worn – If the nut’s threads are excessively worn or damaged, replace with a new properly sized nut.
  3. Re-torque when disturbed – Anytime the terminal nut is loosened, re-torque it to spec when re-installing.
  4. Protect terminals – Keep the posts clean and maintain a light coat of dielectric grease to prevent corrosion issues.
  5. Avoid impacts – Prevent damage to the battery posts and deformation of the nuts by avoiding tool impacts.

Proper battery terminal nut maintenance ensures your connections remain clean, tight, and corrosion free for uninterrupted power delivery.

What Size Are Car Battery Terminal Nuts?

The most common car battery terminal nut sizes are 5/16″-18 and M6. The 5/16″-18 nut has a 5/16 inch diameter and 18 threads per inch. This fits a standard SAE battery post. The M6 nut is a 6mm diameter metric size nut that fits many modern battery posts. 

While these are the two dominant sizes, some larger batteries use 3/8″-16 or M8 terminal nuts. Smaller batteries may use 1/4″-20 or M5 sizes. Always check your battery specifications to determine the proper terminal nut size. Using an improperly sized nut risks loose connections or damage to the battery post.

What Size Are Battery Terminal Studs?

Battery terminal studs are the posts that the cable connections attach to, and their size needs to match the terminal nut. Common stud sizes are 5/16″ and 6mm in diameter, matching the prevalent 5/16″-18 and M6 nuts. Larger batteries may have 3/8″ or 8mm studs, while smaller batteries can have 1/4″ or 5mm studs. 

Studs are often tapered, being wider at the base where they connect to the battery. The tapering allows the terminal nut to firmly clamp the battery cable ring terminal to the stud. Properly sized studs and nuts ensure a secure electrical connection.

What Nuts Are Used On Battery Terminals?

The most widely used nuts on battery terminals are the 5/16″-18 and M6 sizes. The 5/16″-18 is an 18 thread per inch nut with a 5/16 inch inner diameter that fits traditional SAE battery posts. The M6 is a 6mm inner diameter metric nut used on many modern batteries. 

While these two sizes are predominant, larger 3/8″-16 or M8 nuts may be found on heavy duty batteries, while smaller 1/4″-20 or M5 nuts can be used with small lower capacity batteries. Always verify your specific battery’s stud size to select the properly matched terminal nut for a robust connection.

What Size Socket Do I Need To Remove A Battery Terminal?

Most battery terminal nuts are either 5/16″ or 10mm, so you’ll need a 1/2″ or 10mm socket to remove them in most cases. A universal socket wrench can also work if you are unsure of the size. Avoid using pliers or adjustable wrenches which may round off the nut. Break loose the nut manually before using the socket wrench. 

Once detached, you can then disconnect the battery cable and remove the nut completely. Reinstalling the nut just finger tight before final torque with the socket wrench ensures a proper snug fit.


Installing properly sized terminal nuts on your vehicle’s battery is critical to maintaining a solid electrical connection for optimal starting and operation. Use the common metric and SAE nut sizes described to identify the correct fit for your battery’s posts. Adhere to recommended best practices for installation like proper torquing.

And be diligent with regular terminal maintenance and inspection to prevent problems. Equipping your battery with the right terminal nut size provides assurance that your vehicle’s electrical system will function at peak performance.

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Ammar Masoud

I have had a long and fulfilling career in the automotive industry, primarily with Honda and Acura. With 15 years of experience as a Honda service technician, I became highly skilled in repair and maintenance, gaining a deep understanding of these vehicles. After many years in the automotive field, I decided to embark on a second career in industrial manufacturing. It was a significant change, but I found that the skills I had honed in the automotive industry were incredibly valuable in my new role. In my current position in industrial manufacturing, the demand for quality workmanship and meticulous attention to detail is paramount. Fortunately, these are traits that I have cultivated throughout my years in the automotive industry. I take pride in applying these skills to meet the high standards expected in the manufacturing sector.