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I've frequently seen this strange little plastic gizmo (circled in the image) and wondered what its purpose is. I'm tired of wondering -- do any of you know? What is it even called? (Don't ask how long it took to find that image...)

Not all cars have them, but I've seen them on 80's cars and new ones, cheap micro cars and "respectable" sedans, but never on really nice cars. It's certainly not a window guide, and I doubt it's aerodynamic. In this picture it seems to extend backwards behind the rubber trim, but I've mostly seen them extend outwards a bit. The whole thing is no bigger than a sugar cube, and is affixed to the frame of the door (doesn't attach to the window, or even touch it).

Image Source

  • Good question! :D No clue, lol! Commented Jul 17, 2014 at 14:37
  • I still could not find in the Internet any plausible reasons for those things. " window alignment guides" doesn't buy it. In Brazil, there were never a single car ever having those tabs. I have never had any car with "window alignment problems" during whatever speed I was while closing the window, and I already had more than ten different cars at different price ranges, big and small from many regional manufacturers such as GM, VW and Fiat. I'm still expecting to see a auto manufact. reply for what are those things. Air/rain/noise deflector also don't buy me. Commented Feb 10, 2018 at 15:19
  • Maybe it's for future compatibility for sidewindow washers lol!
    – Bart
    Commented Feb 11, 2018 at 16:15

1 Answer 1


It is a guide for the window as it closes. It is only needed for closing the window when traveling at higher speeds as the airflow sucks the window outward. Why you see it on cheaper cars probably has to do with the thickness of the glass and the build of the window frame.

  • Exactly. It is also the thing that gets pried out of position when a bad person wants to steal things from your car. I was never able to get ours precisely back in shape on our old Honda.
    – Bob Cross
    Commented Jul 18, 2014 at 0:51
  • Thank you, I would probably never have considered that. I'll have to take your word for it -- I'm not going to attempt to experimentally verify it.
    – KlaymenDK
    Commented Jul 18, 2014 at 7:42

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