Jigs and holders and gauges and whatnot are necessities for catenary construction. That thing with the plastic strip is a pole height gauge. The plain block is a wire height block/gauge thingy. The flat one on the track is a drilling jig that (hopefully) will guide correctly spaced and square mounting holes. The styrene sheet nestles the jig into the gauge of the track; the gauge will be held in place temporarily with a screw during drilling.