In order to know which size of Adapta-Cap™ is the correct size for your bottle, you need to know what the neck size of your bottle is in millimeters (mm). The neck size is measured from the outside of the threads on your bottle to the outside of the threads on the opposite side of your bottle (as shown below).
*Size F is for a longer-neck bottle.
You can do this either by measuring with a ruler or tapemeasure that is marked in millimeters, or, if you don't have a millimeter ruler, you can compare the neck with regular U.S. coins to determine what the neck size is.
To measure with a ruler, first take the cap off of your bottle to expose the bottle's threads. Second, measure the distance between the outside of the threads on opposite sides of the bottle (As shown above).
If you don't have a ruler or tapemeasure that measures in millimeters, you can compare the neck to regular U.S. coins to determine the size. First, remove the cap from your bottle to expose the threads. Second, line up one edge of a coin with one of the outer edges of the threads on your bottle. Third, use the chart below to help determine what size the neck is on your bottle.