This 500mL Rapid-Flow™ series 291 bottletop filter unit consists of a polystyrene housing and a 75mm/0.2µm SFCA membrane filter. The sterile disposable tissue culture filter unit securely screws onto media bottles with 33mm neck sizes. Allows vacuum filtration of liquid directly into sterile bottles. CAUTION: Use only sterile bottles designed for use with vacuum. Always use safety shield during vacuum procedures. This product is not intended for use in direct patient care or diagnostic procedures. Yellow collar. Material: polystyrene housing and a SFCA membrane. Capacity: 500mL. Membrane diameter: 75mm. Pore size: 0.2µm. Bottle neck size: 33mm. 12/Case. Nalgene®#: 291-3320.