Extension clamps allow placement of apparatus at various distances from the frame or rod. Two-prong clamps are designed to hold straight-sided glassware such as burets, beakers, flask necks,etc. Three-prong clamps are more versatile for irregularly shaped items. Single adjust clamps have one stationary prong and one adjustable. With dual adjust clamps, both prongs are adjustable. All clamps come with non-slip vinyl sleeves and require a separate clamp holder. (See Clamp Holders ).