Hi, this will be my first purchase with the robot shop and I’d like to know how I can request the variations I’m ordering 2 x 28mm diameter brushed DC motors with planetary gearboxes to operate at 17 RPM. In the description it states they can be customised and shaft size can be altered, I would like to have mine increased from 6mm to 8mm how and when can I make this customer request during the ordering process?