This cap fits over the barb outlet on regulators and VIPR cylinders. We also have patented hose barb caps which are designed with ribs to prevent the user from installing a nasal cannula over the hose barb cover without first removing it.  It is also vented to allow for small amounts of oxygen to weep out without building up pressure and forcing the barb cover off.  We have hose barb covers available in three different colors.  Green - ACM 446;  Red - ACM 416; and Black - ACM 204.  We have a red, non-vented cap with smooth sides that can be used for other things as well.  The part number is ACM 345 NV.  We also have matching DISS Connection Caps for the red and green hose barb covers.