In the engine compartment, there's a capped A/C line (high side) near the fuse box. It's a black plastic cap on an aluminum tube. I need a cap as mine apparently fell off. I looked it up and it says it has an M10 thread. But when I look at the tube, there are no threads, so I'm confused. Can anyone pull / unthread your cap to see if it actually threads or snaps off please?