regarding du bush clearence.

Well, first of all, you might want to give a lot more information.

Then, there's this web site, GlobalSpec, that has links to suppliers - like GBB, for example - that could give you the answer.

But, assuming you mean 25.500 mm, try +0.013/-0.000 mm for the bushing bore. That, of course, is backwards since you should start with the bushing bore and throw the tolerance on the shaft, but...

RPM? Lubricant? Type of Bushing? ..

Design of bearing is a complicated business (assuming your bush is a journal bearing). Since the pre-load on it will depend on final operating condition. At that the minimum end-play must exist to avoid damage and metal to metal contact.

I usually leave it to designers

Sorry missed the DU part, for these, about 25mm the recommended clearance is between 0.114mm to 0.01mm, so you can design the shaft accordingly.