Hella 355123002 Vented Disc Brake Rotor 312mm 6x120

The Hella 355123002 is a vented disc brake rotor built for straightforward replacement when your old rotors are worn, scored, or warped. It's a one-piece casting in gray iron, machined on the braking surfaces and finished with a zinc coating on the areas the pads don't sweep. Nothing exotic here. Just a solid, correctly-dimensioned rotor that bolts on and does its job. If you've replaced rotors before, this one installs the same way any direct-fit disc does.

The numbers matter on a brake rotor, so here they are. The disc measures 312mm across the outside diameter with a 24mm nominal thickness. Overall height comes in at 73-1/2mm from the mounting face. It's drilled for a 6 x 120mm wheel bolt pattern and rides on a 79mm hub bore. Those four figures, outside diameter, thickness, bolt pattern, and hub size, are what determine whether a rotor fits, so check them against your vehicle before you order.

Why vented? A vented rotor has cooling vanes cast between two friction faces, and those vanes pull air through the disc as the wheel turns. That airflow carries heat away from the braking surface. Heat is the enemy of consistent braking. When a rotor can't shed it fast enough, the pads start to fade and the pedal goes soft. The vented design here gives the rotor more thermal mass and a clear path for that heat to escape, which keeps your stopping power steady through repeated hard stops, long downhill grades, or a loaded vehicle. Solid rotors are fine on lighter, low-heat applications, but a vented disc like this one is what you want anywhere the brakes see real, sustained work.

The zinc coating is the other detail worth knowing about. Bare cast iron rusts fast, and while the braking surface stays clean because the pads wipe it every time you brake, the hat, the edges, and the vent openings don't get that treatment. Left bare, they bloom orange within a week and look rough behind an open wheel. The zinc coating holds that surface rust off, so the rotor looks clean long after install and the non-swept areas hold up better over the years.

This rotor is sold as a single. Brakes work as a pair across an axle, and you always want matched rotors left and right, so plan on ordering two if you're doing a full axle. If you're just replacing one damaged rotor, one is all you need, but it's good practice to do both sides together so braking stays even side to side.

A word on fitment. The 6 x 120mm bolt pattern with a 79mm hub bore is used across a range of vehicles, and the only reliable way to confirm this is the right rotor is to match the part number, 355123002, to your specific year, make, and model. Don't guess based on diameter alone. Two rotors can share an outside diameter and still differ in thickness, hub bore, or bolt pattern, and any one of those mismatches means it won't mount correctly. When in doubt, cross-reference the part number with your parts catalog first.

When you install it, treat the pads and rotors as a set. Fresh rotors against worn pads never bed in cleanly, so new pads are worth doing at the same time. Clean the hub face so the new rotor seats flat against it, torque the wheel to spec, and bed the brakes in with a series of moderate stops before you lean on them hard. Skip the bed-in and you risk uneven pad transfer, which shows up later as a pulsing pedal under braking. Do it right and this rotor will give you clean, quiet, predictable stopping for the life of the pads.