I'm trying to save an old Trek and need to remove the bottom bracket.

The crankset says FC-M361 but when I google that it says that's a square taper bottom bracket. This surely doesn't looks like a square taper. How do I remove it and what's it called?

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I just realised that my crank removal tool cant do this type of square taper. I have been using this for 10+ years on many bikes and it has always worked.

My old crank tool

Update 2

It is an octalink. My neighbour had a tool and removal was straight away.


  • 1
    The more I look at photo three, the more I see octalink splines. So something doesn’t add up yet. If so it Would just require a slightly different crank puller
    – Swifty
    Apr 24, 2019 at 15:26
  • Ok! That mould make sense! Because I have been using square tapers for many years and it has always worked with my tool.
    – Ola
    Apr 24, 2019 at 16:46
  • Glad it’s sorted. Did you take off both sides yet? Not that the interface on each side could be different to the other. The mystery remains that googling FC M361 shows square taper designs, perhaps they’ve updated the design since yours was made and reverted to square taper on more recent M361. Just speculating though
    – Swifty
    Apr 24, 2019 at 19:02
  • Nathan’s answer to this question has some helpful tool tips if you feel the need to do some shopping
    – Swifty
    Apr 24, 2019 at 19:07
  • 1
    @Swifty Yes, I think they updated to a square taper. This one certainly has octalink on both sides. I just removed both + removed the bb. Not much rust inside the BB shell :)
    – Ola
    Apr 25, 2019 at 5:46

1 Answer 1


I think what is confusing you is that the square hole cannot be seen in the crank with the retaining bolt removed. It seems this model of crank has a circular flange at the outboard end of the square hole for the bolt head to bear on.

Regardless of what the axle-crank interface is, the cranks are removed with a crank puller tool that threads into the retaining bolt hole in the axle and the larger threads in the crank, and pulls the two apart.

DO NOT attempt to get the cranks off any other way, you will damage the square taper interface in the alloy crank arm. (Someone asked a question here once who had levered his cranks off with a crowbar, and totally trashed them.)

You also need a special tool to remove the cartridge bottom bracket. There a ton of help available on the web. Personally I think Park Tool's pages and youtube videos are the most detailed and comprehensive.

Removing 3-piece cranks

Removing cartridge BB

  • Thanks! The strange with this one was that when I google the crankset it said it should be a square taper but this one actually is an octalink. I guess they have updated the design (back to square taper)?
    – Ola
    Apr 25, 2019 at 6:32

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