Park Tool's article on headset servicing states the following (emphasis mine):

... If the headset is using bearing retainers, check the orientation of the retainers before installing. Inspect the metal cage that retains the ball bearings. The cage traps each ball with a hook. Look for the open side of the ball retaining hook. This open side of the cage should face the cone shaped race, not the cup shaped race. ...

-Park Tools, Threadless Headset Service, Feb 2023, https://www.parktool.com/en-us/blog/repair-help/threadless-headset-service

I'm sure that Park Tool's description is obvious to more experienced minds, but I find it a bit confusing.

I feel Park Tool's article changes subject between two sentences. They go from talking about the ball retaining hook to talking about the cage, and I'm not entirely clear what they're attempting to describe as the "open" side. See here a view of one side of my ball bearing retaining cage I've labeled "side 1":

a photo of bicycle ball bearings in a retention cage with text overlaid that says "side 1"

And see here the other side of the cage I've labeled "side 2":

a photo of bicycle ball bearings in a retention cage with text overlaid that says "side 1"

Although it seems I could just as easily use loose bearings or go through trial and error...

... It is also possible to replace retainer ball bearing with loose bearings. ...

... If in doubt, install the cage, and place the race inside and turn. If the cage is correct, it will feel smooth. ...

... I was hoping to understand the terminology here. Which is the "open" side of the retention cage in this case? Is there perhaps another way to describe which side is open vs not open to help less-experienced people like me?

1 Answer 1


There is a ball retaining hook between each ball. The open side would be where we can see a discontinuity (or opening) in the circular metal shape forming the hook. See the difference from this Wheels MFG picture (the open side is on the right):

enter image description here

Zoomed in so we can see more clearly the hook shape on its open side:

enter image description here

  • 1
    So, from the original post - side 2 is the open side.
    – David D
    Commented Mar 1, 2023 at 16:21
  • And you can use loose balls in a headset as well if you continue to have binding issues before all play is removed. You'll require more bearing balls than are in a retainer. The correct number being the race being completely full minus one.
    – Jeff
    Commented Mar 8, 2023 at 11:01

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