Fit for Needle Bearing

25 mm, plus clearance per the bearing manufacturer's recommendation.

I'd consult Machinery's Handbook.

In the catalogues of needle ring suppliers are such values indicated as function of working conditions. Do not forget the surface hardness, the layer thickness and the roughness as well as the cylindricity, all those geometric and quality parameters are important for the application.

Normally when manufacturers make needle bearings, there may be a variance between the needle rollers and their contact surfaces....However, the ID and OD will be manufactured within tolerance. If you plan to remove the IR from an existing bearing, you may be looking for problems. Contact your bearing manufacturer and inquire what shaft size they would recommend. They may want to make the shaft for you so it matches the needle ID envelop as a set.