With KEL-F Luer hub.A septum to be pierced with these PTFE needles must be punctured with a hollow SS needle. The PTFE needle is then threaded through. After threading, the SS needle is withdrawn, allowing the septum to seal around the PTFE needle.For 20 ga PTFE use Z126756 (14 ga SS); 18 ga PTFE use Z126764 (13 ga SS); 16 ga PTFE use Z126772 (12 ga SS).