dummy - GT2 16tooth and 16toothless idler

I downloaded a GT2 pully from somewhere, I thought it was accurate.
I discovered that not only were some of it's dimensions different from the actual idlers I had in my possession, but that the flanges and channels around the bore were completely incorrect.
When designing I often rely on the accuracy of these small dimensions... eg: how big a washer, bolthead or spacer can be before it is no longer bearing only on the inner flange and therefore causes friction on the outer (spinning) component