CE Smith Trailer, 27648, 60" Post Guide-On with l-Beam Mounting Kit. These Post Guide-Ons allow you to see the location of your trailer when it's under water. ÃÂ Pre-galvanised steel parts are stamped from a sheet of steel after it has already been galvanised. The edges of the pre-galvanised parts often lose their zinc coating during the stamping process. Because of the thinness of the coating less than 1 mm and the fact that the edges remain exposed, pre-galvanised parts can begin to oxidise and rust quickly, so its recommended that they be primed and painted.