Got a new frameset, don't know why I need this split ring collar? I can work out all the bits of the semi integrated headset, the star fangled nut for the steerer, but I can't see why I need this? It has similar diameter to the steerer tube, is it a spacer? I don't get it! :/ ![enter image description here](

That looks like the compression ring for a threadless headset.

![enter image description here](
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