20mm Crimp Caps with Clear PTFE/Gray Butyl Rubber Septa. SORT: Product Price Default. 20mm Aluminum Crimp Cap (silver), 9.5mm hole, with Clear PTFE/Gray Butyl Rubber Septum, pk.100. 20mm Aluminum Pressure Release Crimp Cap (silver), 8mm hole, with Clear PTFE/Gray Butyl Rubber Septum, pk.100. Part Number: TF-C4020-39A.