This cap is made specifically for the threaded DISS fitting found on oxygen cylinders with a built in regulator.  Often called VIPR (Valve Integrated Pressure Regulator) cylinders.  This cap protects the inside of the DISS valve from dirt, debris, and other contamination.  It also keeps the poppet from being depressed should the cylinder lean over into something.  This cap slips over the DISS fitting and is red in color.  It is also available in green (Part Number ACM 205).   We also have a DISS cap that is threaded. The part numbers for those are ACM 201 (Green) and ACM 202 (Red).

Qty 500 per bag