Well as you can see in the photos the lead nut wraps 4/5ths around the lead screw. This allows the bottom to be exposed for the last 1/5th. This rides on the roller bearing and not binding just resting. The nut can easily pass over the supports while engaged for the full length. Also the modular desigh allows for any length screw. While traveling the nut is kept centered by the two plates gliding down both sides of the support beam below. Till next time .....and thanks for your support ....LOL