Does anyone have a measurement for the inner diameter required for the washer that you can add to the slipper plate? I'm at work right now and wanted to pick this up on my way home....

I know someone said that due to a chroming process, they may not all fit, even if they are supposedly the same size...but that can be simply solved by getting washers that are not chromed! Or is there a major advantage to having chromed washers?