Roof rack end plug.

Thickness on the filler struts is 1.8mm. Adjust your side layers to make these parts solid. I did 3 top, 3 bottom and 2 side perimeters with 0.45mm nozzle.
Fit a 40mm x 4mm self tapping stainless steel screw to each end to hold the end caps in case it gets whacked and delaminated. It's a good push fit on my roof rack.