Hundreds Of Products Ready Today. Dispatch/Collection Base Mount Or Side Mount? The Bucket Seat Fitting Stack Explained
Frames, runners and side mounts, in the order they bolt up
"I have found the seat I want. What else do I need to actually bolt it in?" That question comes over the counter and down the phone every week, usually with a Sparco found in a sale or a Corbeau out of a project that never happened attached to it. Cameron answers it the same way every time: first tell me whether the seat is base mount or side mount, because everything else follows from that. Subframe, frame, rail, runner, slider, bracket: the trade uses the words loosely and the internet uses them interchangeably, so he ends up drawing the same diagram down the phone most weeks.
Garreth is blunter about it: never let a seat go out without knowing what it is landing on, because the forty quid of steel between the shell and the floor decides whether the six hundred quid seat works at all. This page is the whole answer written down, with the three bolt patterns drawn to scale so you can see which brands cross over and which never will. Ten minutes here and your seat order arrives as one delivery that bolts together first time.
- A full install is the seat plus up to three more parts: a car specific subframe, an optional sliding runner, and side mounts
- Sparco and OMP seats share one 345mm x 271mm base pattern, and Corbeau shells are drilled for two patterns
- Cobra use their own 291mm x 330mm pattern, and Cobra subframes are drilled for Cobra seats only
- The sliding runner is its own product, so price a build as seat, frame and runner
- Every mount and runner on this page is in stock, and Cameron talks customers through the stack most days
The stack, from the floor up
Every bucket seat install is the same four layers, and half of them are optional depending on the build. The car floor carries a subframe made for your exact car, because no two cars put their captive nuts in the same place. On top of that goes a sliding runner if the seat position needs to move, and on top of that the seat attaches either through side mounts bolted to its flanks or straight down through its own base.
The full stack from the floor up, drawn as an assembly order. Plenty of builds skip a layer: a fixed race install often has no runner, and a base mount seat needs no side mounts because the shell bolts straight down. The order never changes though, and pricing a build means pricing every layer your car needs.
Subframe
The car specific layer. Bolts to your floor using the original seat points. Also sold as a frame or a base frame, and it is the part people mean when they say rails, most of the time.
Sliding runner
The adjuster. A pair of locking rails that let the seat move for different drivers. Also called sliders or a runner kit. Skip it and the seat bolts up fixed, which suits a one driver car.
Side mounts
Steel or alloy plates that grip a fixed bucket through the threaded holes in its flanks. Tall, long and low versions exist to move the seat where you need it.
Base mount
No plates at all: the seat has a flat bottom with a bolt pattern drilled in, and it lands straight onto the frame or runners. Most recliners and a fair few buckets mount this way.
Which does my seat use? A two minute check
If the seat is already in front of you, you do not need a spec sheet to work this out. Four checks with your hands and a tape settle it, and they are the same four Cameron talks people through on the phone.
- Look at the flanks of the seatThreaded holes down each side, roughly in line with your hip, mean a side mount seat. Smooth sides with nothing threaded mean it is base mount only.
- Turn it over and look underneathA flat floor with threaded holes near the corners is a base mount. Bare shell with no threads anywhere means the seat can only hang from its sides.
- Measure between the hole centresBase pattern: measure across the seat and front to back, then find it in the table further down this page. Side mount: measure front to back along one flank.
- Check the bolt size before you buy bracketsPut a bolt through the hole. M8 is the industry norm and M10 is the Corbeau exception, and this one detail decides whether an off the shelf bracket lines up at all.
Bolt size is the detail nobody thinks to check, and it is the one that turns a Saturday morning job into a whole Saturday. The threads in the flank of the shell are fixed, so it is always the bracket that has to change to suit the seat. Everything else on this page assumes M8 unless we say otherwise.
Base mount and side mount: the question that decides everything
Before any part goes in a basket, settle which interface your seat uses. Side mount seats have threaded holes through each flank and nothing useful underneath. Base mount seats have a drilled floor and smooth sides. Some shells, like the Sparco Sprint and a run of OMP club seats, carry both, which is why the same seat shows up in fixed race builds and road builds alike.
The two mounting interfaces, drawn to scale
Side mount
Base mount
The two interfaces, drawn to scale from published figures: side mount seats take M8 fixings at about 290mm front to rear on the Sparco shells that publish it, and base mount seats sit on a 345mm wide pattern, the figure every sliding runner kit we list quotes. Your seat has one of these, sometimes both, and it decides every other part you buy.
The three bolt patterns, and who fits whose frame
Base mount seats meet their frame on a drilled pattern, and there are three of them across the brands we stock. This is the single most useful fact on this page: Sparco and OMP share a pattern, so an OMP seat drops onto a Sparco frame and the other way round, even where a listing only names one brand. Corbeau drill their shells for two patterns. Cobra sit on their own spacing, and a Cobra subframe is drilled for a Cobra seat only, so keep Cobra builds all Cobra below the shell.
The three base patterns in our seat attribute data, drawn to scale. Corbeau shells are the clever ones: drilled for both the 291mm x 330mm and the 345mm x 271mm pattern, so they land on either footprint. These are the patterns behind our Fixing Bolt Pattern filter, and behind most of the phone calls this page exists to save you.
| Brand | Base pattern | Fits |
|---|---|---|
| Sparco | 345mm x 271mm | Sparco frames, OMP frames |
| OMP | 345mm x 271mm | OMP frames, Sparco frames |
| Corbeau | 291mm x 330mm and 345mm x 271mm | Drilled for both, so either footprint |
| Cobra | 291mm x 330mm | Cobra subframes only |
| Recaro | 405mm x 290mm | OMP universal flat plates carry this second pattern; Sparco frames do not |
From our own seat attribute data across the range, confirmed while we attributed every Sparco and OMP frame in the catalogue. Recaro side mount buckets like the Pole Position and Profi are the exception to the whole table: they attach through brackets made for that seat family, so match the bracket to the seat, never to the pattern.
The runner is a third product, and the one people forget
The subframe bolts to the floor. The runner goes between the subframe and the seat, and it is always its own product with its own price. Quote a build as seat plus frame and the invoice grows when the runner turns up, so we price every adjustable build as seat, frame and runner from the start.
Garreth would skip the runner on any car with one regular driver. A fixed seat sits solid, costs less, and you set the position once with the mount holes. It also drops the seat lower in the car, which the tall drivers among us care about more than the adjustment.
One trap worth naming: our Sparco runner listing says runners will not fit side mount seats, and that is true at the seat to runner face. Side mount builds that need adjustment put the runner lower in the stack instead, which is what our Clio 197 seat height post walks through on a real car. Runner kits are also often priced per seat, so check whether you are buying one or a pair before you order for both sides.
What the hardware actually costs
The seat is the number everyone budgets for and the hardware is the number that surprises them. Here is the honest picture for one seat. The subframe is the variable: it is made per car, and a common hatchback is a good deal cheaper to sort than a Porsche.
| Layer | What it is | Price including VAT |
|---|---|---|
| Subframe | Car specific, bolts to your floor | About £166 to £330 across the cars we priced |
| Side mounts | Only if the seat mounts by its flanks | £31.80 to £58.74 |
| Sliding runner, one seat | Only if you want adjustment | £41.94 |
| Sliding runner, both seats | The same kit priced as a pair | £78.00 |
| Adaption bars | Only if the seat and frame patterns differ | £47.40 |
| Bolt pack | The fixings, when they are not in the box | £23.98 |
| Fixed side mount build on a common hatchback: subframe plus side mounts, roughly £200 to £225 on top of the seat | ||
| The same build with adjustment: add the runner, roughly £240 to £270 on top of the seat | ||
Prices pulled from our own listings on 19 August 2026 and shown including VAT, so treat them as a guide and check the live figure before you budget. The subframe range covers the cars we happened to price that day, from an M2 Motorsport Scirocco frame at the low end to a PCI Racing Porsche frame at the top. Ring us with your car for the real number, because that one line moves more than everything else added together.
The universal parts, and where to find your frame
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From £29.00 Excl. VAT Select options This product has multiple variants. The options may be chosen on the product page
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From £39.00 Excl. VAT Select options This product has multiple variants. The options may be chosen on the product page
Those eight are counter picks, not the whole shelf. They are the parts we reach for most often, chosen to show what each layer of the stack looks like and what it costs. The full choice lives in side mounts, sliding runners and the wider fitting equipment range. If nothing here matches your seat, that is normal, and it is what the phone is for.
Common questions
Will an OMP seat bolt onto a Sparco frame?
Yes. Both brands drill the same 345mm x 271mm base pattern, so the seats swap between the two frame ranges even where a listing only names its own brand.
Will a Recaro bolt onto a Sparco frame?
Not directly. Recaro base seats sit on a wider 405mm x 290mm pattern that Sparco frames do not carry. OMP universal flat plates are drilled for both patterns, and the Endurance multi point brackets cover 405mm centres too. Recaro side mount buckets are a different case again: they take brackets made for that seat family, so ring us with the exact model.
My seat is a Corbeau. What is different?
The side mount bolts are M10 where the rest of the industry uses M8, so brackets that come pre drilled for M8 will not take the bolts without being opened up. The base pattern is the friendly part: Corbeau shells are drilled for both common patterns, so they land on more frames than most. Tell us it is a Corbeau at the order stage.
Can I put a side mount seat on a base mount frame?
Usually, with the right bridging part between the side mounts and the flat plate. Which part depends on the frame, so send us the frame listing and the seat and Cameron will confirm the combination before you order either.
Do I need a sliding runner?
Only if the seat position has to change. One driver, one position: bolt it fixed and spend the runner money on trim. Shared car or track days with an instructor: fit the runner and buy it in the same order, since it changes the fixing hardware you need.
Are the fixing bolts in the box?
It varies by brand and listing more than it should, and it is the most annoying way to lose a weekend. Tell us the full stack when you order and we make sure the hardware to connect every layer goes in the same parcel, including a bolt pack if the parts you have chosen do not bring their own.
How much of this can I fit myself?
Most of it, if you are comfortable working under a seat with hand tools and you are methodical about torque. The parts are designed to bolt to points that already exist in the car. Where people come unstuck is buying the wrong middle layer, which is the whole reason this page exists.
That is the whole trick to this page. Cameron does the seat to frame to runner match several times a day, he opens the product photos so you do not have to, and the parts arrive as one order that bolts together first time.
Where to go next
If your question is seat height, our tall and long side mounts guide covers moving a seat up, down and backwards in the car, and the Clio 197 post shows a full stack solving a real problem. If you have not chosen the seat yet, our sizing guide starts one step earlier. Ring 0115 9893488 with the car and the seat, and we will spec the rest of the stack while you are on the phone.