Back pack (110) specially designed to hold a 5 lb. or 2.5 lb. CO2 cylinder. Comes with one 5lb. Aluminum CO2 cylinder (104B), also equipped with 4 nozzle spray boom (601C-AN), 0-60 psi pressure guage on boom (174), twin gauge pressure regulator (J062KS), 3.5 ft. air hose (407AA), spray hose (408A). Spray hose and air hose have industrial disconnects. (Model D is priced without a container.) Select a container of your choice as a separate item. ---- Size of spray container will determine each specific unit. Determine the total area sprayed per each treatment. Based on spray volume per unit acre or hectare you can figure the minimum size of spray container. Your plot size and volume may vary so various sizes of containers may be required. If the complete spray units do not meet your requirements, specific parts may be substituted. Example, you may want to purchase a Model GS sprayer but want to replace part #201S (28mm brass spray header with SS drop tube) with part #202 (28mm brass spray header used inverted). Simply order a model GS and state that you want to substitute part #202 for part #201S. The same principle applies to the spray boom. The boom in all spray units comes with 19" or 48 centimeter spacing. If you want or desire different spacing (Example: 15" spacing), simply specify the desired nozzle spacing.