Gray PTFE/Red Butyl Septa, Φ17.5*1.6mm. CA001. 18mm Magnetic Precision Screw Metal Cap, 8mm Centre Hole. SACA001. Blue PTFE/White Silicone Septa, 18mm Magnetic Precision Screw Metal Cap, 8mm Centre Hole. SACA002-II. Red PTFE/White Silicone Septa, 18mm Magnetic Precision Screw Metal Cap, 8mm Centre Hole. SACA003-II.