I was working on my bicycle, a 2021 Domane SL5, and laid it on the ground. When I picked it up, I saw a small metal ring on the ground underneath. I don’t know for certain if the metal piece came off the bike, but what do you think? Is this a part from the bike?

I was installing a DuoTrap sensor. I thought maybe it came from the rubber grommet or part of the installation kit for the sensor but I haven’t been able to confirm; installing the sensor seemed to be fine so I’m not sure if it’s a needed part.

the top of it the flat of it

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    Looks too clean to be off of my bike Aug 10, 2021 at 21:38
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    FYI, DuoTrap is a speed/cadence sensor that can be integrated into Trek frames. I'm not sure how the arrangement works, but could this metal item have come from the door that you plug the DuoTrap sensor into?
    – Weiwen Ng
    Aug 10, 2021 at 23:02
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    @WeiwenNg it might have come from the duo-trap rubber thing. The instructions mention a 2mm grommet. I wonder if the sensor is even installed correctly? Aug 10, 2021 at 23:20
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    Looks like a cable pulley to me, or something to guide a cable round a bend. I’m not sure how it would have been mounted to a bike though.
    – Dan K
    Aug 17, 2021 at 19:59
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    Hard to tell without a scale, but it looks like the fastening that joins a disc rotor to its spider.
    – bertie
    Jan 3, 2022 at 16:33

1 Answer 1


If you check this video: Youtube, "Installing a Bontrager Duotrap S Sensor on a Trek Domane":

At 1:32, the guy who's installing the Duotrap holds a rubber bushing/gasket/seal-thingey and with the thumb and forefinger of his right hand he's holding onto the front outer part of that seal where you can see a metal spacer that probably makes the Duotrap sit at the correct distance from the frame?

BR Magnus

  • 3
    Whoa, that will probably earn me a badge for "Thread revival of 2023"...
    – MagnusK
    Nov 18, 2023 at 15:40
  • Magnus - maybe not a badge but a bounty for answering an otherwise unanswered and difficult question. Keep it up !
    – Criggie
    Nov 20, 2023 at 10:54

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