What those numbers mean
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30.15 mm (ID) → fits a 1 1/8” steerer tube
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41 mm (OD) → fits the frame’s bearing seat (common IS41 standard)
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6.5 mm height → stack height—important for proper preload
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45° / 45° angles → angular contact surfaces (must match exactly)
This is typically referred to as an R408 / MH-P03 bearing, one of the most common sizes for integrated headsets on road and MTB bikes.
Compatibility tips (don’t skip this)
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41 mm vs 41.8 mm is NOT interchangeable
Even a 0.8 mm difference won’t fit properly.
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45°/45° vs 36°/45° matters
Wrong angle = poor seating, creaking, premature wear
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6.5 mm vs 7–8 mm height
Small differences can affect headset preload and fork/frame gap
Alternatives with same spec (if you can’t find ZERO)
Here are equivalent R408-type bearings with the same dimensions:
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KCNC Headset Bearing R408 41x30.1x6.5mm – lightweight alloy option
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Veyga Headset Bearing P03/R408 41x30x6.5mm – budget-friendly
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Gurpil 41x30.15x6.5mm 45/45 Bearing – stainless option for durability
They’re all functionally interchangeable as long as the dimensions and angles match exactly.
Quick sanity check before buying
If you still have the old bearing, look for laser markings like:
