How can I solve drill size DRC error in Cadsoft Eagle ?
In the Hole properties there is no options to adjust drill, only 0.02 is the one option.

Is manual routing or wire-width reduction are the only options to avoid 'clearance' error in PCB ?

 

One more doubt.
Does it is possible to use multiple wire widths on the same PCB ?

 

How can I solve drill size DRC error in Cadsoft Eagle ?
In the Hole properties there is no options to adjust drill, only 0.02 is the one option.

You did not have the "centered" box checked, so the offending via/pad is not shown. In my version of Eagle (4.16r2) I have to un-check and then re-check the Centered box to get it to show me the which hole(s) is/are undersized.

If it's a via, I fix the drill size right there on the board. If it's a pad on a part, I fix the problem in the library by updating the package for the part; then start to add another of the same part to the schematic. Eagle will detect that the library has been updated, and ask if you wish to update the part in your schematic. Click yes. Then cancel the addition of the part. Then run DRC again.

Is manual routing or wire-width reduction are the only options to avoid 'clearance' error in PCB ?

You need to have 8 mil minimum clearance between items on the board; traces, pads, vias, etc. Most PCB manufacturers won't make a board that has less than that much clearance between items.

In another thread, you auto-routed the board, and then increased the trace width. That may have caused problems. You can manually change the trace widths where they go between pads/vias.

 

One more doubt.
Does it is possible to use multiple wire widths on the same PCB ?

Certainly.

You can even set that up in the Autorouter, if you care to write that many rules. Since I don't have the Ripup/Route module in my registered version, I won't be of much help there.

However, when you are manually routing, you can change trace widths "on the fly" anytime you wish.