Perko Clam Shell Ventilator 4" Chrome 0339-DP0-CHR by Perko $56.99 1 2 3 4 5 6 7 8 9 10+ Quantity Quantity Add to cart Perko Clam Shell Ventilator #9-0339DP0CHR Base: 4" x 3-3/4" Cut Out: 1-5/8" x 2-1/2" Chrome Plated Brass Screw size is 6.