Customer Question: What Size Bolts Do Bucket Seats and Brackets Require?
Customer question, seat fitting
We are asked this a lot: what size bolts do bucket seats and their brackets need? The short answer is M8 for nearly everything. Almost all aftermarket fixed back bucket seats, reclining sport seats, side mounts and runners are made for M8 bolts, which are 8mm in diameter.
The one exception is Corbeau's side mounted fixed back bucket seats, which use M10. Corbeau's base mounted reclining seats use M8 like everyone else. Below we go through each joint in a typical seat install, the Corbeau exception, and how the frame bolts to the car.
- Most bucket seats, recliners, side mounts and runners use M8 bolts
- Corbeau side mounted fixed back bucket seats use M10
- Corbeau reclining seats use M8
- Corbeau side mount seats need M10 side mounts made for them
- The frame usually bolts to the car with the original seat bolts or those supplied with the frame
- Replace seat bolts that have been in and out many times or through a heavy impact
What is on this page
M8: the standard for seats and brackets
For the great majority of aftermarket seats and brackets, the bolt is M8: 8mm in diameter, normally with the standard 1.25mm coarse thread. Sparco, OMP, Recaro, Bride, Cobra, Mirco and Sabelt seats, and Corbeau’s reclining seats, all use M8 at their mounting points.
- Seat to side mount. A side mounted bucket usually takes four M8 bolts, two each side, into the seat’s side mounting points.
- Seat to base or runner. A base mounted seat usually takes four M8 bolts into threaded holes underneath.
- Runners. Runners are drilled for M8, both where they meet the seat and where they meet the frame.
- Side mount to frame. Side mounts normally bolt down to the frame or runners with M8 bolts.
Because most makers have settled on M8, side mounts, runners and bolt kits from different makers often share it. That does not mean every part fits every seat: hole spacings still differ, so check the spacing as well as the bolt size.
M8 bolt packs
We list two Endurance Motorsport M8 packs for seat side mounts. The steel pack is plain, correct grade steel hardware. The titanium pack uses Grade 5 titanium, around 43% lighter than steel per bolt, with a hex or T40 Torx head and seven anodised colours. The saving is grams, not kilograms, but on a stripped car, or if you want the bolts to match the seat, it is a nice finish. Matching titanium nuts are available in blue and gold.
Garreth’s advice is to keep a spare pack. Seat bolts see shock loads, and they are worth replacing if the car has had a heavy impact or the bolts have been in and out many times. New bolts are cheap; a stripped thread in a seat shell is not.
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From £23.98 Incl. VATPayPal CreditSelect options This product has multiple variants. The options may be chosen on the product page
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The exception: Corbeau side mounted seats use M10
Corbeau’s fixed back bucket seats that side mount use M10 threads, not M8. This covers seats such as the Forza, LS2 and Pro. Their side mounting points are also at their own positions, so they need side mounts made for Corbeau.
The Endurance Motorsport steel M10 side mounts are drilled for Corbeau’s M10 fixing. A standalone M8 side mount would need its holes altered to take an M10 bolt, and we do not recommend doing that. On M2 Motorsport or PCI Racing frame kits, whose side mounts are drilled for M8, Corbeau side mounted seats no longer bolt straight on: the holes need drilling out slightly for M10, a small modification, so ask us if you are unsure.
Corbeau’s reclining sport seats are base mounted and use M8, so if you have a Corbeau recliner you will not need anything unusual. Older Corbeau seats made before the mid 2000s sometimes used a different side hole spacing, so if you have an older seat, measure between the side holes before ordering mounts. Our guide to Corbeau M10 fittings goes into more detail.
Mixing brands
Keep a Corbeau side mount seat on M10 mounts made for it, with M10 bolts. Do not try to fit an M10 seat to M8 mounts, or an M8 seat to M10 mounts with packing washers: the fit will not be right and the joint will not be as strong as it should be.
If one seat in the car is a Corbeau and the other is not, that is fine: use a pair of M10 mounts on the Corbeau side and standard M8 mounts on the other. If you are unsure what a seat takes, tell us the make and model and we will check.
Side mount and base mount: where the bolts go
Side mounted seats. Most fixed back buckets have mounting points on their sides. The side mounts bolt to the seat, then down to runners or the frame:
- Seat to side mount: four bolts, M8 on most seats, M10 on a Corbeau.
- Side mount to runner or frame: four bolts, normally M8.
Base mounted seats. Reclining seats and some buckets mount underneath. Four bolts go up through the runner or frame into the seat base, M8 for all the brands above, Corbeau recliners included. If runners are fitted, they bolt to the frame too.
Our guide to seat runners covers the runner part of the stack and which widths suit which seats.
Bolting the frame to the car
The joint between the frame and the car is different. It uses the car’s own seat mounting points, and those are whatever the car maker chose, often larger than M8. A vehicle specific frame is made to line up with those points.
- Keep the bolts from the original seats. Many frames are designed to go in with them.
- If the frame comes with its own hardware, or the car has studs, follow the frame maker’s instructions.
- Do not substitute random bolts at the floor. They may not match the thread in the car and may not be strong enough.
- Tighten everything properly. If in doubt about the torque, use the car maker’s figure for the seat mounts.
Bolt sizes at a glance
| Joint | Bolt size |
|---|---|
| Side mount bucket seat to side mount, most brands | M8 |
| Corbeau side mount bucket seat to side mount | M10 |
| Reclining or base mount seat to runner or frame, including Corbeau | M8 |
| Standard side mount to runner or frame | M8 |
| Runner to frame | M8 |
| Frame to car floor | The car's seat bolts, or those supplied with the frame |
What size bolts do bucket seats use?
Nearly all use M8; Corbeau side mounted fixed back buckets are the exception and use M10.
Do Corbeau reclining seats use M10 bolts?
No. Corbeau recliners are base mounted and use M8 like other brands.
Can I fit a Corbeau bucket seat to M8 side mounts?
We do not recommend it; use M10 side mounts made for Corbeau seats.
What bolts hold the seat frame to the car?
Usually the car’s original seat bolts, or the hardware supplied with the frame; follow the frame maker’s instructions.
Are titanium seat bolts worth it?
They save a little weight and look good; the steel pack does the same job for less.
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Most seatsM8, except Corbeau buckets
M8 for nearly every seat and bracket, M10 for Corbeau side mounted buckets.
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