There isn’t a single universal size for starter mounting bolts. Sizes vary by vehicle, engine, and mounting configuration. In practice, you’ll commonly encounter bolts around 8–10 mm in diameter (roughly 5/16" to 3/8"), with fine thread pitches such as 1.25 or 1.5, and lengths typically in the 20–40 mm range. Always confirm the exact size from your vehicle’s service manual or by measuring the replacement hardware.
Why sizes vary
The starter sits at the junction of the engine and transmission bell housing, and manufacturers tailor the mount to the engine block and flywheel housing. Variations in bolt diameter, thread pitch, length, and the number of mounting points reflect different engine designs, mounting brackets, and torque requirements.
How to determine the correct size for your vehicle
To avoid incorrect fasteners, use a verification process before purchase or reassembly. The steps below help you confirm the exact bolt size and type for your car.
- Check your owner’s manual or the vehicle’s service manual or the exact bolt specification in the OEM parts catalog for the starter mounting bolts.
- If manuals aren’t available, inspect the current bolts or the mounting holes: measure the bolt diameter with calipers and count the number of threads per unit length (thread pitch) with a thread gauge.
- Consult an auto parts retailer or the manufacturer’s online parts fiche using the VIN to pull the exact bolt specification for your exact model and year.
- Confirm the bolt length and shank type (plain shank vs. flange vs. shoulder) to ensure proper clearance and seating against the bell housing.
- Use bolts of the correct grade and quality (e.g., high-strength metric or SAE bolts as specified) and torque to the recommended specification in the workshop manual.
Following these steps reduces the risk of cross-threading, misalignment, or inadequate torque on startup hardware.
Common sizes you might encounter
Note: actual bolt size depends on the vehicle. The ranges below reflect common patterns across many cars and trucks.
- Metric engines: often M8 × 1.25 or M10 × 1.5, with bolt lengths around 20–35 mm;
- Imperial/SAE engines (older or some US models): commonly 5/16"–3/8" diameter with fine threads (roughly 18–24 tpi), lengths around 3/4" to 1-1/2" (19–38 mm).
When in doubt, rely on the vehicle’s official documentation or consult a qualified technician.
Summary
The size of starter mounting bolts is not universal and depends on the specific vehicle and engine design. Typical ranges include 8–10 mm diameter (metric) or 5/16"–3/8" (imperial), with various thread pitches and lengths. Always verify with the service manual or OEM parts information, measure the bolts if needed, and replace with the correct grade and length while torquing to specification.
What size are starter mounting bolts?
Specifications
| Thread Diameter | 5/8 in |
|---|---|
| Starter Mounting Bolt Thread Size | 3/8"-16 |
| Threads Per Inch | 16 |
| Starter Bolt Hex Size | Not Applicable |
| Starter Mounting Bolt Length | 4 5/8" |
How to tell if bolt is M6 or M8?
If the thread is specified simply as M6, it's a standard pitch. Standard pitch would be fully written as M6 x 1.0. Fine would be M6 x 0.8. Note, though, that the pitch varies with the thread diameter – so a standard M8 thread is M8 x 1.25 and a fine thread M8 x 1.0.
What size stud is a LS starter?
Main Power Connection: The main power connection on most LS starters is a large hex stud, typically a 13mm nut. Ls starters can pulls hundreds of amps of current so using a sufficient wire size is CRITICAL. This is a place when bigger is better and nothing smaller than a 2 gauge wire should be used.
Is a #10 bolt 10mm?
The size designation helps in identifying the right bolt for the specific application, ensuring a secure and reliable fastening. Overview: M10 bolts have a 10mm diameter, making them suitable for heavy-duty applications.