This is the product we've always used with our Tucked Radiator Kits. Works fantastically when welded directly to the upper neck. Provides the ideal way to fill the system and purge the air in applications where no other means are possible. CNC machined from 6061 billet aluminum.
Includes a 1/8" NPT x 1/4" hose overflow fitting. Total height is only 2.75" and the overall length is 4.5". The cap is pressure rated to 16lbs // 1.08 bar