Hella 355123122 Vented Disc Brake Rotor, 320mm 6x112

The Hella 355123122 is a vented, one-piece disc brake rotor, and it's built the way Hella builds everything: fit it, forget it, and let it do its job for years. This is the friction surface that turns your vehicle's momentum into heat every time you press the pedal, so the material, the cooling, and the fit all matter. Hella's part number here is 355123122, and it's sold as a single rotor.

Start with the size. The rotor measures 320 mm across the outside diameter, which is a little over 12.5 inches, with a 28 mm nominal thickness. That's a large swept area, and a large swept area means more surface for the pads to grab and more mass to soak up heat before the rotor gets hot enough to fade. The 68 mm hub size is the center bore, the machined opening that slides over your hub so the rotor runs true. Get that seating right and you won't chase phantom vibrations later.

The wheel bolt pattern is 6 x 112 mm. That's a six-lug pattern on a 112 mm circle, and it's the single most important number to confirm before you order. Hold this rotor up against your current one, count the lugs, measure the circle, and match the 320 mm diameter and 28 mm thickness. If all four numbers line up, bolt pattern, hub bore, diameter, and thickness, you're in the right place. If any one of them is off, it's the wrong rotor for that corner, and no amount of muscle will make it fit correctly.

Now the design. This is a vented rotor, not a solid one. Vented means there are internal cooling vanes cast between the two friction faces, and those vanes act like a centrifugal fan when the wheel spins. Air pulls through the middle and carries heat away. That's what you want on a vehicle that sees real stopping loads, towing, grades, stop-and-go traffic, or just a heavier platform, because heat is the enemy of consistent braking. A cooler rotor holds its bite and keeps the pedal feel firm.

The casting is one-piece gray cast iron. One-piece means the hat and the friction ring are a single casting, so there's no separate hardware to loosen or corrode between the two. Gray cast iron is the standard material for brake rotors for good reason: it damps vibration well, it machines cleanly, and it handles thermal cycling day after day. Hella finishes the non-friction areas with a zinc coating, which is the gray you'll see on the hat and edges. That coating fights the surface rust that blooms on bare cast iron the first time it gets wet, so the rotor looks clean behind an open wheel and stays that way longer.

A few install notes from people who've done this a hundred times. Replace rotors in pairs, both sides of the same axle, even if only one looks worn. Braking is a balance act left to right, and a fresh rotor on one side with a tired one on the other pulls the vehicle under hard braking. Fit new pads at the same time. New pads on an old glazed rotor, or old pads on a fresh rotor, never seat properly and you lose braking performance you paid for. And once everything's bolted up, bed the pads in: a series of moderate stops from moderate speed that lays an even transfer layer of pad material onto the rotor face. Skip that step and you can end up with uneven deposits and a pulsing pedal.

Because this rotor ships as a single, order two if you're doing a full axle, which is the right way to do it. Keep the box until you've confirmed fitment on the car. If the numbers match your application, this is a straightforward, durable replacement that'll give you clean, quiet, predictable braking for a long time.