The POLYCAST® 651 catch basin becomes the 751 catch basin with the addition of a heavy duty cast iron frame. This frame allows heavier traffic to run across the catch basin, and prevent weathering on the side of the basin. The same 12×24 inch grates can fit into the catch basin with or without the frame. If you have a run of the other POLYCAST® channels with this catch basin, you will need to match the configuration between frames. If the channels have the cast iron frame, the catch basin will require one as well.