Clamp is required to attach the psychrometer to a plant stem. It is available in 4 sizes:
Small Stem Clamp (PSYS-C37) for stem sizes between 10 and 37 mm in diameter
Medium Stem Clamp (PSYS-C55) for stems sized between 10 and 55 mm in diameter
Large Stem Clamp (PSYS-C77) for stem sizes between 30 and 77 mm in diameter
Extra-large Stem Clamp (PSYS-C125) for stem sizes between 78 and 125mm in diameter