Place the belt idler pulley in its place.

Use M3x20 Socket Cap Screw and M3 nut to fix the idle pulley. Do not too tighten, idle pulley should turn freely.

Mount 2x M3x20 Socket Cap Secrews and 2x M3 Nuts and tighten them equally. Leave 5mm distance between the idle pulley piece and extrusion mount piece.

Use a M6x14 Socket Cap Screw to mount the tensioner. Ensure that idler pulley and GT2 motor pulley are aligned. This is not the latest alignment, so do not final tighten.