Measure the height in millimeteres of baluster (note: the height does not include the joints above and below the baluster, you may have to remove some paint in order to see where the joint begins).
In all cases the number after the pre-fix is the baluster height in millimetres.
Navigate to the approriate page for your baluster type and height (eg to match a baluster which is 327mm tall with a single round bowl you should look in the n200-400mm range).
Once at the appropriate page you can search using thumbnails, remember to search 20mm above and below your decided height, as joints can be increased or flanges trimmed down.
Click on the 'pdf' icon to bring up a larger, printable image of the selected baluster listing more dimensions.
Example: S470 = 470mm high baluster with one square bowl (do not include joints in your measurements) search 20mm above and below your measured height.