Search our head gasket collection for one engine and you can get a page of listings that look almost identical. Same maker, same engine code, same photo. The differences are packed into a few characters of each title: 87mm or 88mm, .040 or .051, MLS or MLX, LHS or RHS. Those few characters decide whether the gasket seals your engine or sits in a drawer. This guide takes a multi-layer steel (MLS) head gasket listing apart, one detail at a time, using real listings from our catalog, so you know which numbers you have to bring to the order and which ones belong to your engine builder.
Take one title apart
Here is a real listing: Cometic Honda K20/K24 87mm Head Gasket .040 inch MLS Head Gasket. Read left to right, it tells you five things:
- Engine family: Honda K20/K24.
- Bore: 87mm, the size of the hole the gasket is cut for at each cylinder.
- Thickness: .040 inch.
- Construction: MLS, multi-layer steel.
- Side: nothing, because an inline four has one head and needs one gasket.
Every head gasket listing carries some version of those five details, though not always in that order. The sections below cover each one, plus the engine qualifiers that sometimes hide in the middle of a title.
Bore: match the cylinders you have, not the car they came in
The bore figure in the title is the diameter the gasket's combustion openings are cut for. It has to suit the cylinders in your block as they are now, which is not always what the car left the factory with. If the block has been bored oversize for bigger pistons, the gasket follows the new bore.
That is why a single engine family can carry a long run of sizes. For the K20/K24 we list Cometic gaskets cut for 86, 87, 87.5, 88, 89 and 90mm bores. For Honda B-series blocks there are 81, 81.5, 82, 84, 84.5 and 85mm versions. On the Subaru side, the EJ25 DOHC gaskets are listed at 100mm while the EJ255/EJ257 gaskets are listed at 101mm. The This Part Fits table cannot tell these apart, because it lists vehicles, not bore sizes. Your machine shop's measurement or the piston spec sheet for your build is the number to match.
Thickness: a number your builder picks, not one we can
Thickness is the detail people most want a quick answer on, and the one we will not guess for you. A thicker gasket holds the head further from the block, which changes compression and the space between the piston and the head. The right figure depends on your pistons, the deck height, whether the block or head has been resurfaced, and the boost and fuel you plan to run. That calculation belongs to whoever is building the engine.
What this guide can do is show you how wide the choice is, so you know to ask. These are the ranges we currently list for a few common platforms:
| Engine family | Bore in the title | Thicknesses listed |
|---|---|---|
| Honda K20/K24 | 86 to 90mm | .027, .030, .036, .040, .045, .051, .060 in (varies by bore) |
| Honda B-series, including hybrids | 81 to 85mm | .030, .036, .040, .051 in |
| Subaru EJ25 DOHC | 100mm | .027, .030, .040, .045, .051, .060 in |
| Subaru EJ255/EJ257 | 101mm | .036, .040, .051, .056 in, plus an MLX version |
| Subaru FA20 (BRZ, FR-S, 86) | 89.5mm | .032, .040, .042, .050, .052 in, left and right sold separately |
| Mini 1.6L turbo (N14/N18) | 78mm | .036, .040, .044, .048, .052 in |
Two habits help here. First, read the description as well as the title. Many Cometic listings state a compressed operating thickness in the first lines of the description; the EJ255/EJ257 MLX gasket, for example, has no thickness in its title at all and gives 0.032 inch in the description. Second, if the title and the description seem to give different figures, stop and email us before ordering. A thickness mismatch is not something to settle by picking the number you prefer.
Construction: what MLS, MLX and "stopper" tell you
MLS means multi-layer steel. The Cometic listings describe it as three to five layers of stainless steel, with the outer layers embossed and coated on both sides with Viton, a rubber coating rated heat resistant to 250 °C (482 °F). The center or shim layer is uncoated stainless steel, and it is the layer that can be varied to make the different thicknesses in the table above. The listings also say MLS gaskets need no sealants and suit both aluminum heads on aluminum blocks and aluminum heads on cast iron blocks.
MLX is Cometic's multi-layer stopper design. Per the listing copy, it adds an integrated stopper layer for combustion chamber sealing, giving improved clamp load around the cylinder without increasing bore distortion, and it needs no sealants or re-torque. The FA20, N55 and Mini gaskets we carry are MLX, as is one of the EJ257 options. The N55 .052 inch MLX gasket describes its shim as increasing clamp load around the combustion chamber to improve sealing around the open-deck block.
Other labels appear too. The Evo X 88mm .050 gasket is titled "Stopper Head Gasket". One EJ257 option is marked MLS-5, and a BMW S58 listing is marked DST. When a construction label is not explained in the listing, ask us what it means for your build rather than assuming it is an upgrade or a downgrade.
Side: one head or two
Inline engines have one cylinder head and take one head gasket. Flat engines like the Subaru FA20 and V engines like the Nissan VQ have two heads, and many of their gaskets are sold one side per listing. You will see this written as LHS and RHS (left-hand side, right-hand side) or as "Left" and "Right".
The Nissan VQ30DE/VQ35DE gasket is a good example: the LHS and RHS are separate listings with separate part numbers. The FA20 gaskets work the same way, starting with the .042 inch MLX LHS. On these engines, a complete job means one of each side, in the same thickness and bore, unless your builder has a reason to do otherwise. If a side marking ever looks contradictory, check the part number with us before you order.
Engine qualifiers hiding in the middle of the title
Some of the most important words sit between the engine name and the size. A few real examples:
- "Non VQ30DE-K" on the VQ gaskets rules out one specific version of the engine even though the family name matches.
- "Gen3" on another VQ35/37 gasket separates it from the earlier VQ35DE listings.
- "Motor" vs "Turbo" and "SOHC" vs "DOHC" on the Subaru EJ22 and EJ25 listings separate versions of the same engine family.
- "Hybrid LS/VTEC" on Honda B-series gaskets means a non-VTEC block with a VTEC head, as the 84mm .051 inch hybrid listing states. "LS" here refers to the Honda B18 engine found in the Integra LS. It has nothing to do with GM's LS V8.
If one of these qualifiers applies to your engine, it matters more than any row in the fitment table. Our guide to checking engine part fitment before you order covers reading the This Part Fits table itself.
Not every MLS gasket is a head gasket
Cometic makes other gaskets in multi-layer steel, and their titles share the same vocabulary. The Honda B-series exhaust manifold gasket is listed as ".030 inch MLS" with a port size of 1.850 by 1.340 inch. A pair of port dimensions in the title is the giveaway: that is an exhaust gasket, not a head gasket. Watch for it, because a few exhaust listings also carry the words "Head Gasket" in their titles. Gasket kits work the other way round. The Cometic Street Pro EJ257 kit says "Without Head Gasket" in its title, so the head gasket is a separate order. You can browse the full range in our Head Gaskets collection.
Where block reinforcement changes the shopping order
A head gasket only seals as well as the surfaces on either side of it stay put. On an open-deck block, the cylinder tops stand free in the water jacket, and under boost they can move. A better gasket does not stop that movement, and neither do head studs, which handle the clamping side of the job. Our explainer on what head studs fix and what block filler fixes goes through the split, and studs for most engine codes are in Head Stud & Bolt Kits.
If you plan to support the deck with EPOXY54, choose your head gasket before pour day. EPOXY54 gives an open-deck block closed-deck strength without machining, with 21,000 psi compressive strength and thermal expansion closely matching aluminum, and it is a DIY install in 5 steps. With a Partial Fill, which fills the top ¾ inch of the water jacket and keeps OEM coolant capability, the head gasket is the template for drilling the coolant passages back through the cured epoxy, so you want the exact gasket you will run in hand. Dry Block fills the whole jacket and is for track use only. The EPOXY54 Installation Guide walks through the steps.
If you are replacing a gasket that already failed, work out why it failed first. Our guide to reading a blown head gasket on a boosted engine covers the clues, and the glossary of engine block terms explains words like fire ring and bore distortion that come up in gasket listings.
Bring these to the order
Before you add a head gasket to the cart, have your engine code and version, your finished bore size, the thickness your builder specified, and whether your engine needs one gasket or a left and right pair. Then check the title qualifiers, read the first lines of the description, and confirm your vehicle in the This Part Fits table. If any of those disagree, email support@epoxy54.com with the listing link and your build details, and we will check it with you.