Both the Calibrex 520 and 521 Bottle Top Dispensers come standard with a 32 mm screw thread, and included with each dispenser are three polypropylene bottle neck adapters (28, 40, and 45 mm for the 520 model; and 38, 40, 45 mm for the 521 model). If replacement or different size adapters in different materials are needed they can be purchased separately.
