No, this product is an assembled screw-hole cap with a PTFE/silicone septum. There is no indication it is gas-tight. It can be used with any vials with 13-425 threading.
For gas-tight applications, the magnetic screw cap for the CTC instrument, such as SU860101, is currently offered. This cap features precision threading with numerous threads to force the septa against the vial making it gas-tight.
Please see the product in the link below: https://www.sigmaaldrich.com/product/supelco/su860101
Vials suitable for this cap are listed in the Related Products section of the product page.
Another option is the Mininert® Valve screw caps, such as product 33300. It enhanced sealing ability for containing most volatile liquids and gases at low pressures:
Link: https://www.sigmaaldrich.com/product/supelco/33300
Vials suitable for this cap are listed in the Related Products section of the product page.
