Replacement CO2 cylinders used in inflatable life vests.  Replace with cylinder of the same CO2 mass (weight) and thread size. 

#540  16 grams, 3/8" threads
#352  18 grams, 3/8" threads*
#351  24 grams, 1/2" threads
#350  25 grams, 3/8" threads
#472  29 grams, 1/2" threads (Mil-Spec)
#480  31 grams, 1/2" threads
#484  33 grams, 1/2" threads

* Item #352 subject to 25 piece minimum order.