[Barrykgerdes]

I havn't looked at mine for some time but I think it is about 18".
However if you are suffering from instability with your current bearing size I don't think you will get any improvement with a larger bearing.

What you need to do is increase the thickness of the base with some 1/2" ply. Also do the same with the rocker box.

Next use a better pivot bolt that is firmly attached to the base and has a thrust race attached to the the rocker box to hold it to the base.

I have made new pivot bolts of different custom designs for a few DOB mounts that do just this and it makes the azimuth bearing very rigid.

Barry