If you chose an eccentric sander, the next step is to determine the diameter of the sanding pad. With a 125mm sanding pad, you have slightly less reach than with the larger versions. But a 125mm eccentric sander can come in handy for your planned job. Narrow surfaces, such as the back of a chair or the bars of a fence, can be sanded in a more controlled manner with this sanding pad size. Make sure to take suitable sandpaper to achieve the desired result into account.