Are All Battery Terminal Bolts the Same?

No—battery terminal bolts are not all the same. They differ by terminal style (top post, side post, stud, or insert), thread size and pitch (metric vs. SAE), length, head type, and material. Common sizes include M5/M6 (motorcycles and small sealed batteries), 3/8″-16 (GM/Delco side-post automotive), 5/16″-18 (marine studs), and various M6, M8, 1/4″-20, and 5/16″-18 fasteners used on cable clamps for top-post automotive batteries. Using the wrong bolt can strip threads, loosen connections, or damage the battery case.

Why They’re Not the Same

Battery systems are built around different standards for different applications and regions. Automotive top-post batteries rely on clamp bolts that vary by the cable-end hardware; GM-style side-post batteries use a standardized internal thread; marine batteries often add stainless studs; motorcycles and UPS/SLA batteries use small metric fasteners into captive nuts. Each use case drives different thread forms, lengths, and corrosion-resistant materials.

Common Terminal Types and Their Typical Bolts

Automotive Top-Post (SAE/JIS) Clamps

Most passenger vehicles use tapered lead posts with cable clamps tightened by a bolt and nut. The bolt is part of the clamp and is not standardized across all vehicles.

The following list outlines typical fastener sizes and notes for these clamps.

• Clamp pinch bolts: commonly M6 x 1.0, M8 x 1.25, 1/4″-20, or 5/16″-18 depending on the clamp design and brand.
• Head styles vary: hex, flanged, or with captive nuts; length varies with clamp thickness.
• Torque is modest to avoid deforming the lead post—typically 5–9 N·m (4–7 lb·ft), but always check the vehicle or clamp manufacturer’s spec.

Because these bolts are part of aftermarket or OEM cable assemblies, replacing like-for-like is safest; substituting threads or lengths risks poor clamping or stripped hardware.

GM/Delco Side-Post Automotive

Side-post batteries use an internal threaded insert in the battery case for a direct bolt connection.

The following list describes the standard thread and best practices.

• Standard thread: 3/8″-16 UNC for the battery’s internal insert on virtually all GM-style side-post units.
• Bolt length matters: too long can bottom out and crack the insert or case; typical overall bolt length is around 0.6–0.8 in (15–20 mm), but follow the battery maker’s guidance.
• Typical torque: about 13 N·m (10 lb·ft), unless the battery label specifies otherwise.
• Accessory/junction studs are available (longer, with external stud) for multiple ring terminals.

Sticking to the correct 3/8″-16 bolt and length is critical on side-post batteries; avoid metric bolts, which can partially engage and damage the threads.

Marine Dual-Terminal Batteries

Marine batteries often provide both standard posts and threaded studs to secure ring terminals for accessories.

The points below summarize the common stud sizing and care.

• Accessory studs are typically 5/16″-18 with stainless nuts and lock washers.
• Torque commonly falls in the 9–12 N·m (7–9 lb·ft) range; overtightening can strip the stud or crush lugs.
• Some European marine batteries may use M8 studs; verify before replacing hardware.

Because marine environments accelerate corrosion, matching thread size and using marine-grade stainless or tinned copper hardware is important for long-term reliability.

Motorcycle, ATV, Powersports, Lawn & Garden, and Small SLA/UPS

Smaller batteries typically use captured square nuts inside the terminal with ring-lug bolts.

The list below covers the most common threads and installation tips.

• Common sizes: M6 x 1.0 and M5 x 0.8; length usually 10–16 mm depending on lug stack-up.
• Torque: roughly 2–5 N·m (M5 on the low end, M6 on the high end). Check the battery spec sticker.
• Some lawn & garden equipment may use 1/4″-20 instead of metric; confirm before threading.
• Spacers or “nut elevators” may be needed so the bolt can reach the captive nut inside the terminal.

These small fasteners strip easily; use correct length and avoid mixing metric and SAE hardware.

Materials and Corrosion Resistance

Fastener material affects both longevity and electrical performance, especially where corrosion can raise resistance and cause starting issues.

The following points explain common materials and when to use them.

• Steel, zinc-plated: common and economical; adequate for most automotive clamps but can corrode without protective grease.
• Stainless steel (A2/A4): preferred for marine and harsh environments; slightly less conductive but acceptable for clamping functions. Use anti-seize sparingly to prevent galling on studs.
• Brass/bronze: excellent corrosion resistance and conductivity; often found in aftermarket lugs and some terminal posts, less common as the actual clamp bolt.
• Lead inserts/washers: side-post bolts may include lead or sealing washers to improve contact and seal; replace like-for-like.

Whichever material you choose, apply dielectric grease on exposed metal after tightening to slow corrosion; avoid greasing threads that require precise torque unless the spec assumes lubrication.

How to Identify the Right Bolt

Confirming thread, length, and head type before replacement helps avoid damage or unreliable connections.

Use the checklist below to verify and source the correct hardware.

• Identify terminal style: top-post clamp, side-post, stud, or insert (check the battery and cable ends).
• Read the battery label: many list terminal type and torque; marine and powersports labels often show M5/M6 or stud size.
• Measure the thread: use a thread gauge or bring the old bolt; check if it’s metric (M5/M6/M8) or SAE (1/4″-20, 5/16″-18, 3/8″-16).
• Match length: ensure full engagement without bottoming out; include ring lugs and washers in your measurement.
• Check head clearance: some clamps or compartments restrict hex size or require low-profile heads.

When in doubt, take the original bolt to a parts store or reference the vehicle/battery manual; a small mismatch can ruin threads in soft lead or brass inserts.

Torque and Safety Basics

Correct torque and safe handling prevent damage and ensure reliable starting and charging.

The following guidelines cover the essentials most owners need.

• Typical torques: top-post clamp bolts 5–9 N·m; GM side-post 13 N·m; marine 5/16″-18 studs 9–12 N·m; motorcycle M6 3–5 N·m, M5 2–3 N·m.
• Avoid overlength bolts: bottoming out can crack inserts or puncture a cell.
• Disconnect negative (-) first and reconnect it last to reduce short-circuit risk.
• Do not stack too many ring terminals; use a bus bar or proper junction stud if needed.
• Clean contact faces; apply dielectric grease after tightening to protect against corrosion.

These practices help maintain low-resistance connections, protect the battery, and extend system life.

Myths and Clarifications

Several misconceptions persist about battery hardware. Here’s what to know.

The following bullets clarify common points of confusion.

• “All car battery bolts are the same.” False—clamp bolts vary widely; only GM-style side-post threads are largely standardized at 3/8″-16.
• “Stainless bolts always conduct worse.” Stainless is less conductive than copper/brass, but clamp bolts mainly provide mechanical force; the lug/post interface carries the current.
• “Longer is stronger.” Not with batteries—overlength bolts can cause expensive damage.
• “Metric and SAE can be mixed if they feel close.” Cross-threading soft inserts is common and dangerous; always match the thread standard.

Choosing a bolt based on “fit by feel” is risky; proper identification prevents costly failures.

Bottom Line

Battery terminal bolts are not universal. Match the terminal style, thread size/pitch, length, material, and torque to your specific battery and vehicle or equipment. When unsure, reference the battery label or manual and compare to the original hardware.

Summary

Battery terminal bolts vary by application: automotive top-post clamp bolts differ by clamp design; GM side-post uses 3/8″-16; marine studs are typically 5/16″-18; motorcycles and small sealed batteries commonly use M5 or M6. Mixing metric and SAE threads or using the wrong length can strip inserts or damage the case. Verify terminal type, measure threads, match length and material, and tighten to the specified torque for a safe, reliable connection.

What size is the bolt on a battery terminal?

Battery terminal bolt sizes vary, but common types are M6 bolts for top posts and 3/8-16 bolts or M8 bolts for side posts. The specific size depends on the battery’s design, so it is best to check the battery’s specifications or use a socket or wrench that fits the bolt head on your terminal to determine the correct size, such as 10mm or 12mm.
 
To determine your battery terminal bolt size:

1. Visually inspect the bolt: Observe if it’s a metric bolt (with an “M” in the designation) or a standard bolt. 
2. Use a socket or wrench: Try different common sizes, like 10mm or 12mm, or 3/8-inch. 
3. Consult the battery manufacturer: Check your battery’s manual or the manufacturer’s website for exact specifications. 

Common Bolt Types:

• Top-post batteries often use a nut and bolt system where the bolt can be an M6 bolt or similar, with a common 10mm socket size. 
• Side-post batteries commonly use a threaded post with a bolt inserted from the terminal clamp. 
  • Some side posts use a 3/8-16 thread, which is 3/8 inch in diameter with 16 threads per inch, a common “coarse” thread in the US. 
  • Other side-post batteries might use a metric bolt, such as an M8 bolt (8mm diameter). 

Are all battery terminals the same size?

No, battery terminals are not all the same size; they vary in size, shape, and type depending on the application, including differences between automotive and other battery types, as well as variations in terminal design such as the common top post, side post, and L-terminals. For automotive batteries, the most common terminal types are the tapered SAE posts and smaller JIS posts, where the positive terminal is intentionally larger than the negative to prevent accidental reverse connections. 
Common Battery Terminal Types

• SAE Post: The most common type in North America, featuring two tapered lead posts with the positive post being larger than the negative to ensure proper polarity. 
• JIS Post: A smaller version of the SAE post, often found in older Japanese-manufactured cars. 
• Side Post Terminals: Found on some GM and other vehicles, these are recessed female threaded sockets where bolts attach, with both posts having the same size. 
• L-Terminals: These have an L-shaped post with a bolt hole, used on European cars, motorcycles, and other light-duty applications. 
• Faston Tabs: Used on Sealed Lead Acid (SLA) batteries for applications like UPS systems, these are flat blade-type terminals of varying sizes (e.g., F1 and F2). 

Why Terminals Vary

• Preventing Polarity Errors: The most common reason for different terminal sizes (like in SAE and JIS) is to make it physically impossible to connect cables to the wrong terminal, which could damage the electrical system. 
• Application Specifics: Different battery applications require different connection methods. Side posts, L-terminals, and Faston tabs are designed for specific types of connectors and wiring. 
• Vehicle Origin: The origin of a vehicle or its electrical design can dictate the type of terminal used, with standards like SAE and JIS being common in different regions. 

Can you use a regular bolt on a car battery?

Shouldn’t be a problem as long as they’re bare metal. Just be sure to remove the bolts when you’re done so they won’t corrode in place.

Can you use any bolt for a battery terminal?

No, you cannot use any bolt for a battery terminal; the bolt must be the correct metal type, typically brass or stainless steel, and the correct size and thread pitch for the terminal to ensure a secure, electrically conductive connection and prevent corrosion. Using the wrong metal, such as a galvanized or aluminum bolt, can lead to rapid corrosion or even galvanic corrosion issues.
 
Key Considerations

• Material: Use bolts made of brass or stainless steel, as these are resistant to corrosion and provide good conductivity. 
• Galvanic Corrosion: Avoid using bolts made from incompatible metals (like aluminum with steel), as this can accelerate corrosion on the battery terminal and surrounding areas. 
• Size and Thread: Ensure the bolt fits the threaded hole of the terminal correctly, matching the thread pitch and not being too long, which could puncture the battery. 
• Corrosion Prevention: Once the new bolt is in place, apply dielectric grease to the terminals and bolt to protect against moisture and further corrosion. 
• Terminal Type: Be aware that different battery types (e.g., side post vs. top post) use different terminal designs, so you need the correct bolt type for your specific battery. 

Where to Get the Right Bolt

• Auto Parts Stores: Check with an AutoZone or other local auto parts store for the correct type and size of battery terminal bolt, as they carry various options. 
• Manufacturer: Check your battery’s specifications to confirm the bolt size and material you need, notes RELiON batteries. 
• Specialty Battery Suppliers: Online retailers or specialized shops can also provide the correct hardware for your battery.