These are Douglas Fir #1 and btr 12″ x 48″ x 20′ Trestle Mats complete with 4 rods 1-1/4″ diameter,  countersunk both sides, including internal lifting plates for rigging (picture). The internal plates “pop up” out of the surface when used and then retract below the surface when not in use. When building a trestle (or temporary bridge) there is no openings in the surface to cause a trip or safety hazard. In this case our customer is building a temporary work platform (or trestle) from a barge in a river, there is no road access to this remote site. They are doing reclamation work beside the railway.  Important points, these are specified by an engineer to be #1 and btr Douglas Fir timbers due to the weight of a crawler Crane that will be on the trestle.