UPDATE, use 683zz at 3x7x3mm to get enough material to make it strong enough. but really use a metal one with the appropriate dimensions.
I found an issue with my da vinci x idler pulley squeaking, so I replaced the pulley with two 623ZZ (3x10x4mm) ball bearings and this printed part. You can also use 693ZZ (3x8x4mm) or MR63 (3x6x2.5) and make your own pulley.
The issue is detailed here (http://voltivo.com/forum/davinci-hwmods/41-squeaking-and-or-circles-aren-t-round-check-this-56k-warn/reply/7767) and the solution is to replace the pulley with this part and ball bearings (and you may also have to replace the belt tensioner with something like thing:920971 or thing:921117 eventually).
The actual OD for the bearings is 10mm, but I can't seem to get the pulley ID to print right, so I included a couple variations. Just add some tape if it's too loose, heat it up and press fit if it's too tight.
You'll have to lightly hammer out the 3mm rod from the old pulley and into the new bearings since it's such a tight fit. You might also want to use some small m3 washers to prevent the tensioner from pinching this part and adding resistance.
A final untested solution would be to use a premade pulley like this one (http://www.ebay.com/itm/3-x-16T-3mm-Bore-6mm-GT2-Belt-Smooth-Idler-Pulley-with-Bearing-for-3D-Printer-/131459526147?hash=item1e9b992e03:g:QL4AAOSwpDdU7Ybq) which has inset MR63 bearings (3mm ID, 6mm OD, 2.5mm thickness). I couldn't find a listing for less than 3 at a time, but it just so happens that I own 3 da vincis. Make sure to get a smooth one because GT2 is more popular and the these are actually S2M. A "16 tooth" sized pulley (no teeth, just the size of one with 16 teeth) is about the right size for the pulley (smaller so it fits, and not too wide. Again, you'll probably want washers.
added a chamfer so you don't need support material