Flat-Top or Finned-Top OSFP? How to Tell Which Module Your ConnectX-7 Actually Needs

The answer, first

Flat-top goes in the server. Finned-top goes in the switch.

If you're populating an OSFP port on a ConnectX-7 or ConnectX-8 adapter, or a DGX system, you need the flat-top module — Mellanox part MMA4Z00-NS400, which NVIDIA now also numbers 980-9I51S-00NS00, for 400G SR4. (A BlueField-3 DPU is not on that list: BlueField-3 accepts QSFP112 only, never OSFP, and takes the MMA1Z00-NS400 instead. More on that below.)

If you're populating a port on an air-cooled Quantum-2 switch — a QM9700 or QM9790 — you need the finned-top module, part MMA4Z00-NS, which is twin-port and carries 800G as 2 × 400G.

That's the whole rule. The rest of this post is why, what happens when you get it wrong, and the third variant that catches people out.

Why the fins matter

The fins aren't a cooling upgrade. They're a statement about which end of the link the module belongs in.

A ConnectX-7 OSFP port has a heatsink built into the cage. It sits down on top of whatever module you insert. That's why NVIDIA now calls the flat-top form factor RHS — Riding Heat Sink. The equipment's heatsink rides on the module. There is no clearance for a module with its own fins, so a finned module simply won't seat.

An air-cooled switch port has no such heatsink. The module has to bring its own. NVIDIA calls that IHS — Integrated Heat Sink, because the fins are integrated into the module's metal top.

The fins are either on the module or on the equipment. Never both, never neither.

If you learned this as "flat-top and finned-top," you're not out of date — those are still the common names. But NVIDIA's documentation increasingly says RHS and IHS, so it's worth knowing both, because you'll see both in the same procurement thread.

One scope note: all of this is an OSFP question. QSFP112 modules have a single shape, so if someone asks which top style you need on an MMA1Z00-NS400, they are quoting from the wrong family.

What a wrong order actually costs

The finned-top-in-a-NIC mistake is the common one, and it's usually reasoning that sounds right: 800G is a bigger number than 400G, so surely it's the better module. But the twin-port 800G finned module is a switch part. It won't fit the NIC, and the 800G isn't usable at the server end anyway — the ConnectX-7 OSFP port is a 400G port.

The reverse mistake — flat-top in an air-cooled switch — is worse, because the module physically seats. It looks like it worked. There's just no cooling path.

Neither mistake is expensive per unit. Both are expensive at cluster scale, because nobody orders one. They order forty-eight, and the mismatch surfaces on install day.

The canonical topology

The two parts are designed as a pair:

One twin-port finned module in the switch → two MPO-12/APC patch cords → two flat-top modules in two ConnectX-7 servers.

One switch module serves two servers. When you're sizing an order, that's the ratio: for every two server ports, one switch module. The two adapter-side modules can be OSFP, QSFP112, or one of each — the switch module does not care. The cords between them are MPO-12/APC, Type B, female — not the UPC cords from your 100G or 200G fabric, which will not mate with an NDR module at all.

The third variant nobody stocks

Here's the one that isn't in most catalogs.

There is an 800G SR8 module in flat-top — part MMA4Z00-NS-FLT. NVIDIA's documentation for this family is specific about where it goes: flat-top transceivers are required for the DGX H100, while the finned-top 2×400G part is what goes in Quantum-2 and Spectrum-4 switches, where airflow is reduced and the module has to carry its own cooling. The same flat-top logic applies to any deployment where a cold plate or a cage heatsink needs to contact a flat surface and integrated fins would be exactly wrong.

So the full picture is four rows, not two:

If you're populating DGX H100 front cages and someone quoted you the finned part, that quote is wrong. We don't stock the flat-top 800G — we'd rather tell you the part number than sell you the one we have. For a BlueField-3 we do now stock the right answer: the MMA1Z00-NS400 in QSFP112.

Part numbers that look alike but aren't

A few near-misses worth checking your PO against:

• MMA1Z00-NS400 — one character off, and it's QSFP112, a different cage entirely. It will not fit an OSFP port. This is the part a BlueField-3 DPU takes, and the one to order for a ConnectX-7 in its QSFP112 form.
• MMS4X00-NS400 — single-mode DR4 at 1310nm, 500m reach. Different optics, different fiber plant.
• MMS4X00-NM / MMS4X00-NS — the 800G single-mode DR8 variants.

The MMA / MMS prefix is the tell: MMA is multimode, MMS is single-mode. Everything in this post is multimode SR. If your plant is single-mode, none of these are your part — and any seller who doesn't ask which you're running isn't paying attention.

→ Full NVIDIA OSFP part-number crosswalk — every part number in this range mapped to form factor, optics, reach and which end of the link it belongs in.

Why you'll see 50m on one sheet and 100m on another

Worth knowing before you plan a run. NVIDIA qualifies these modules at 50m over OM4 — and 30m over OM3. The SR MSA the optics are built to permits up to 100m over OM4. Both numbers are correct — the standard describes what the optics can do under ideal conditions, and NVIDIA's number is what they will support in an InfiniBand fabric. NVIDIA's twin-port 800G documentation describes straight multimode cables up to 100m and splitter cables up to 50m, which is the same budget described from the cable's end rather than the module's.

The practical part: every additional MPO mating in the path eats optical budget. A 90m run through three patch panels is exactly where link margin quietly disappears. Design to 50m and you keep support parity with NVIDIA and a margin you can troubleshoot.

FAQ

Which OSFP module goes in a ConnectX-7 adapter?
The flat-top (RHS) MMA4Z00-NS400, also numbered 980-9I51S-00NS00, for 400G SR4. The finned-top (IHS) MMA4Z00-NS is the twin-port 800G module for air-cooled Quantum-2 switches such as the QM9700 and QM9790.

Does a BlueField-3 take the flat-top MMA4Z00-NS400?
No. BlueField-3 adapters accept QSFP112 devices only — NVIDIA states that OSFP is not for use in BlueField-3 DPUs. The equivalent part is the MMA1Z00-NS400 in a QSFP112 shell, $549 at Resilient Tec. Same 400G SR4 optics, same MPO-12/APC fiber, different cage — and no flat-top/finned-top question, because QSFP112 has one shape.

How much do the flat-top and finned-top OSFP modules cost?
At Resilient Tec, the flat-top MMA4Z00-NS400 is $579 and the finned-top MMA4Z00-NS is $829. The QSFP112 MMA1Z00-NS400 is $549. All are new compatible modules with a lifetime warranty. (Prices checked October 12, 2026.)

Where can I buy the MMA4Z00-NS400 or MMA4Z00-NS?
Directly from Resilient Tec in Knoxville, Tennessee: MMA4Z00-NS400 — $579 at resilient-tec.com · MMA4Z00-NS — $829 at resilient-tec.com · MMA1Z00-NS400 — $549 at resilient-tec.com

Ready to Buy?

We stock these parts, new, and ship from Knoxville, Tennessee. Lifetime warranty, backed by Resilient Tec. Prices below checked October 12, 2026.

• 400G OSFP SR4 Flat-Top (RHS) — MMA4Z00-NS400 compatible — $579 — the ConnectX-7 / ConnectX-8 / DGX server-side module
• 400G QSFP112 SR4 — MMA1Z00-NS400 compatible — $549 — the BlueField-3 and ConnectX-7 QSFP112 module
• 800G OSFP SR8 Finned-Top (IHS) — MMA4Z00-NS compatible — $829 — the Quantum-2 air-cooled switch-side module
• MPO-12/APC OM4 multimode trunk cable — Type B, female-to-female — $59.00 (1 m) to $139.00 (20 m) — the fiber between them

Populating a cluster? Tell us the port count and we'll quote the pair together. Running single-mode, or building liquid-cooled? Ask — we'd rather point you at the right part than sell you the wrong one.

You Might Also Need

• OSFP DAC cables — when the run is short enough that copper beats optics
• MPO-12/APC vs UPC fiber for NDR optics — the fiber between the two modules above, and why your existing cords won't mate
• QSFP112 stacking cables for DGX Spark and the DGX Spark interconnect reference
• Cat8 and structured cabling for the rest of the rack
• Network switches — Arista, Cisco, HPE/Aruba and Mellanox, new and tested pre-owned