Each has a 3 size barb fitting 3/8", 1/2" & 5/8"

MWT112:  Circle Diffuser Tubing. 

Diffuser Tubing rods

MWT113: 9 inch Rod Diffuser 

MWT114: 12 inch Rod Diffuser (RD-12

MWT115: 15 inch Rod Diffuser 

MWT116: 24 inch Rod Diffuser (RD-24) 

MWT117: 36 inch Rod Diffuser (RD-36)