The front door o-ring in a Stoelting soft serve machine is inserted into the grooves of the dispenser door. It's function is to create a seal between the opening of the freezing cylinder and the dispenser door itself. This prevents any liquid product from leaking out of the freezing cylinder. If leakage is present around the edges of the dispenser door, it could be time to replace your front door o-rings. Fits Stoelting Models: 0111, 0231, 0411, 0431, 0431RC, 238R, E111, E131, E131-YG, F131, F131-YG, F144, F231, F431, SF144, SU444, and U431.