CT Bore Size

[bergerud]

I was making an ER11 adapter for my friend's C machine. I assumed that the bore was going to be a fairly accurate 1/2". I found instead that it was 0.5025". That seems a little large to me. This explains why I could see the bit wobble. I thought it was a poor adapter, but it turns out the adapter is 0.4995" which does seem reasonable. With the side clamping, there is a guaranteed run out of around 0.003". My question is this: Are all of the CT bores this large or did my friend just get a bad one? This is an important question if 3rd party ER adapters were to be made. With the side clamping, such adapters have to be a snug fit. Could some of you measure your bore sizes and post?