The Oriol Plus pad drive comes with a center lock which helps centering the pad and keeps it in place when you lift the machine. Because we ran into difficulty in the past with the rubber doughnut which suppose to even out the variation of the floor pad, we omitted this rubber from the drive block. The reason is because the manufacturer of the this rubber provided us with unpredictable hard and soft rubber doughnuts. By removing this rubber we made the pad driver more stable and predictable. Of course the ultimate evenness of the machine while it is running, will depend on the floor pad. But as we know, many floor pads are NOT even because they are not "woven" and they are not "machined" they are just poured from the hopper onto the conveyor belt and glued together. That is why you can find thickness difference on the same pad as much as 1/4 inch across its diameter. To make matters worst, when the operator leave the floor pad on the floor machine and park it for the day, next time he/she will start the machine, it will wobble like a duck. Because the floor pad by the weight of the machine is compressed on one side and made it uneven. Luckily this drive block can not be squashed (remember, there is NO doughnut) and that help to maintain the machine to run even. On the bottom of the pad drive are the usual hooks to hold the pad in place. Available in 16" or 18".