Can we talk about "center bore" for a minute?

Mike69cuda said

There has been a lot of talk here about hub centering rings without any dimensional data to support their use. So how accurate is a plastic ring? So far I have seen numbers kicked around like 5 to 8 mils being good enough. Two diameters on a ring would need to +/- 2.5 to 4 mills each to make that. Seems like that is pretty tight for a piece of plastic, particularly if it is molded.

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Most metal CNC'd hub centric rings have a true position between the OD & ID of .1mm (.004"). I've never had one off over .013mm (.0005")...

The plastic ones made from Polycarbonate plastic are usually about the same accuracy or close to that.

Some ABS plastic ones are .1 to .3mm (.004"-.012") off, don't buy any of them but the metal CNC'd ones.

True Position isn't given as a + or - tolerance in GD&T manufacturing. It's basically in this case the diameter of the widow the center point of the OD & ID can fall within.