Brass Porthole Mirror 20 w/Nickel Finish. 20 Brass Porthole Mirror w/Nickel Finish Maritime Decor. The 20″ Brass w/Nickel Finish Porthole Mirror measures 20″ in diameter. The Mirror is 13 1/2 in diameter, This also could be used as a window by replacing the Mirror with Glass. Great for Restoration or in Home use. This is a New Item. Item Weight 17 Lbs. _gsrx_vers_804 GS 7.0.8 (804).