Magnetic screw closures N 18 have a more convenient, consistent, and safer sealing process compared to crimping (better reproducibility). Due to the thinner septum (1.5 instead of 3 mm), penetration of the needle is easier and executed with less fragmentation (especially important for SPME applications). They offer a flat surface for the magnet; thus the filled vial cannot drop from the magnet which may be the case with over-crimped vials due to the convexity of the cap.