This chrome plated breather, or oil filler cap, is internally baffled with filter. Very similar to the original equipment breather used on 1965-1967 Chevrolet 396-427 Big Blocks. GM (General Motors) #6421868. Fits valve cover openings with 1.22 inch diameter. Its overall dimensions are 2-1/8 inch tall and 2-1/2 inch in diameter.