Every cap and plug is printed to order in PETG. They are for keeping dirt, water and paint out of open ports and hose ends while a line is off, on the bench or in the parts bin. They are not pressure plugs. Colors let a shop code by size, by machine or by tech. Need a standard we do not list, ORFS, BSPP, SAE O-ring boss or a metric flange? Use the custom request form and we will draw it up.