When a customer buys a Power Base, the hardware kit that comes with the Power Base includes a White Plastic Pulley for the Ball Winder. This pulley has been used since the beginning of the Power Base program in 2008. The very first pulleys were sized to hold belts measuring 3/16" in diameter. That practice ended in 2010 approximately and the design was changed to accommodate a larger 1/4" diameter belt.
If you owned an early power base that used the thinner 3/16" belts, when you upgrade to a new High Torque R-19 motor, you will need to replace the pulley on the ball winder so that it can accommodate the thicker 1/4" belts. All that this means is that the groove for the belt on the pulley is wider and can hold the 1/4" dia. belts.