Rip, I think John meant a bar with 30 mm
sleeves, not the bar itself. Juergen is using 1 inch inner diameter plates (exercise plates) or their European equivalent, and hence is looking for a bar with rotating sleeves that will fit those.
Juergen, consider that a rotating sleeve must add diameter to the section of the bar around which it sits. Barbells with sleeves for 50mm ID plates have that 50 mm sleeve around a 27-30 mm bar that runs nearly the full length of the sleeve, so the 27-30 mm steel bar is bearing the weight. For a bar with a 30 mm grip section, the ends would have to be milled significantly smaller than a 30 mm diameter to fit inside the 30 mm outer diameter sleeves while leaving sufficient sleeve thickness + the bushings/bearings. This would sacrifice far too much structural integrity to be safe for use.
Think also about dumbbells made from these kind of plates (
e.g. the ones Rip discusses here:
https://www.youtube.com/watch?v=V7pVtXPYtGM ). They use sleeves for the hand to grasp and allow the bar stock to rotate inside of them. This is cheaper, but it also reflects the same need - adjustable dumbbells that take this size plate either do not rotate, have a rotating sleeve, or depend on slop between the bar and the plates for rotation. If you're going to stick with these plates, you'll need to get your rotation from something other than the sleeves on the barbell.
The 2"/50mm ID plates and their associated bars are better in the long term for this and many other reasons.