Matala Hakko Air Tube Diffusers are designed to be a drop-in system. The rubber membrane is wrapped around a hollow PVC tube. The air holes are a little larger than other brands, so you get medium-sized bubbles which do not clog and put very little back-pressure on your system. This means very low maintenance and effective aeration system. These must be filled with rocks or gravel in order to be weighted down.
The MTD-300W and 600W are 12" long and 24" long. These are self-weighted 2" diameter tubes with a rubber membrane wrapped around the outside. The MTD-300W and 600W come with 2 separate barbs which must be glued in place. Use regular PVC glue. The barb sizes include a 2 section barb with 5/16" and 3/8" size and a 1/2" barb size.