The Semi-Recessed Valve Cap & Collar functions with the Semi-Recessed Valve Body, p/n's Z60053 & Z60217. 

The cap is what makes the valve fully airtight. 

The cap’s o-ring must be in good condition in order to maintain a proper seal for the inflatable’s air chamber. 

The Cap with Collar includes a new o-ring. 

Make sure to tighten the cap well to keep the tubes fully inflated when on the water.