Handheld deburr / reaming tool.

This tool is the Best option I have found to easily and precisely remove the sharp edge on the inside of the gauge port opening.

To prevent air leaks, removing the sharp edge keeps the o-rings on the valve assembly and the gauge port from being nicked during their installation.  

Directions:  Rotate the blade of the deburr tool clockwise around the entire inside sharp edge of the gauge port opening 5 to 6 times. 

Keep it in your tool box. Also great for removing the sharp edge from other items too. Copper, Iron, Brass, PVC Plumbing Pipes, 3D Printing Plastics, Resin Art, Metal Work etc..