You will likely find out that there are only one or two dart sizes available and that there is not a grade of PVC that will match. Caliber is simply the diameter in hundredths of an inch. Blow guns are made out of aluminum that is stiffer and lighter than PVC. A 1/2 inch is .50 caliber. 1/2 inch is .50 caliber. caliber is measured by fractions of an inch in a decimal format, like 1/4 is .25 caliber, .40 caliber is 4/10, 3/4 is .75 caliber, etc. one caliber = 1 inch.