Slide a M3 washer on a M3x40 screw.

Insert the screw in the top left hole of the x_carriage until it is just protruding from the other side of the extruder_body.

Add a M3 nylon washer on the end of the screw.

Add the extruder_idler in the opening. and push the screw.

Leave a space to insert the second M3 nylon washer.

Insert the second M3 nylon washer and push the screw further to secure it.

Slightly tighten the screw, ensuring that the extruder_idler can still rotate freely.