Yes, there are three holes in the top of the PTFE insert in the mobile phase delivery cap (our catalog number 58820-06) which are threaded for use with standard low pressure male nuts as shown below in the image.

  1. Threaded Holes:
    • All three holes have a ¼-28 thread. This means they are threaded with a ¼-inch diameter and 28 threads per inch.
    • Two of the holes have a 3.4 mm inner diameter (ID), which corresponds to 1/8-inch tubing.
    • The remaining hole has a 1.8 mm ID, suitable for 1/16-inch tubing.
  2. Functionality:
    • The two larger holes (3.4 mm ID) allow for different tubing sizes or venting options.
    • The smaller hole (1.8 mm ID) is designed for use of all capillaries of up to 1/16-inch tubing with low pressure connectors (nuts).


Keeping these caps on the bottles with the tubing through it prevents dust and dirt from getting in and minimizes outgassing and absorption of CO2 from the atmosphere. However, these caps are not designed for applications which require sterility of the bottle’s contents. The caps do not fully seal on mobile phase bottles. They will not allow a vacuum to be created nor will they allow the bottles to be over pressurized which should always be avoided.

Click HERE for mobile phase delivery bottle cap ordering information and pictures