GL45 safety caps are made with PTFE insert inside the cap for maximum inertness on a wide variety of solvents. The GL45 cap is design with the inner body rotates independently of the outer collar to prevent twisting of tubing when the cap is removed or attached. It is design to minimize chemical evaporation. 1 pc/pk. Commonly use on HPLC solvent bottle for use with 3 semi-rigid tubing equal to 1/8¡± outside diameter and 1/4-28 PEEK Fitting for 1/8 OD tubing.