Includes a 3-prong swivel clamp and a boss head clamp holder Made of aluminum alloy body with plastic knobs, the durable, sturdy constructed boss head clamp holder accepts rods up to 16 mm diameter Feature maximum grip size of 87 mm (3.42 inch) and a total length of 270 mm (10.63 inch), this StonyLab 3 prong extension clamp is used to securely hold almost any type of apparatus and glassware with non-slip rubber coated jaws The adjustment screw of clamp helps provide precise pressure regulation and reduce chance of glassware breakage