Screw top vials & caps are recommended for tightest seal & most reproducible headspace results, precision-thread, making them an excellent choice for dependability and ease-of-use. 1] Clear glass Flat bottom vial & PTFE-Silicon septa with Magnetic Screw cap: Part No. 10 ml :-GC10FB07 Pack size: 100 Nos. 20 ml :- GC20FB07.