I am looking to install a dropper post on my Trek Marlin 7 Gen 2 (2021) size XL. I am thinking I want to get a PNW Cascade 150mm. When I went to measure the seatpost to make sure, it stopped before the slight bend in the tube. I believe this is caused by the bottle cage bolts. From searching online, I have read that there may be a piece holding them in from inside the tube, can I remove the bolts at home or should I go to my local shop?

-- thumbdrive

  • Are you asking if you can remove the bolts or remove the eyelets into which the bolts thread?
    – Paul H
    Commented Apr 13 at 0:14
  • Does the 125mm fit? If you can, better to find a seat post that meets you needs than modify the frame.
    – mattnz
    Commented Apr 14 at 1:46
  • Is the frame built for an internally routed dropper cable? I wasn't sure if there was space to route it internally or not .
    – Taylor
    Commented May 18 at 22:49

1 Answer 1


I think the threaded nuts in the seat-tube are nut-serts, which are usually riveted in place. I would take it to the bicycle shop.

I've never used a dropper post but since they have height adjustment, wouldn't one of the PNW models fit into your frame without having to remove the bottle cage nut-serts?

Going by the PNW Cascade webpage diagram the 150mm model, at the minimum insertion into your seat-tube, 110mm, you would have approx.340mm of seat-post above the seat-tube clamp. (E-D+B) 245-110+205=340

For the PNW Cascade 125 mm at the minimum insertion 90mm, you would have approx. 310mm of seat-post above the seat-tube clamp. (E-D+B) 215-90+185=310

Droppers CASCADE measurements

  • Thank you so much! I have no idea what I was thinking. For some reason, I had been measuring from the wrong point in the seatpost, which made me think It was too short and that I needed to remove the threaded nuts. I went back this afternoon and measured from within the seatpost itself and discovered that In in fact do have enough space for the 150 mil dropper.
    – Thumbdrive
    Commented Apr 14 at 19:24
  • Hi Thumbdrive, as long as you have 110mm between your seat tube clamp and the highest threaded nut on your seat tube then it will clear the bottle nuts.
    – MindDBike
    Commented Apr 15 at 5:44

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