My top cap screw bolt is currently stuck in my compression plug, and I'm seeking some advice on how to remove both the broken bolt and the compression plug.

enter image description here

This was the top cap I was using:
It's a weightweenie one piece top cap and top cap bolt.
enter image description here

What happened

My initial installation of the top cap wasn't perfect for the preload.
Symptoms appeared in the form of loose headset and the top cap bolt becomes stuck.

Tried to unscrew top cap but didn't work.
Eventually the T25 top cap bolt stripped.
Used Araldite in the bolt and on my T25 key, left it over 2 nights, still didn't unscrew.

Hence my diagnosis was that during installation, there was cross-threading. But does it explain why it is so insanely difficult to unscrew? Not sure.

Then came the drilling.
My plan was to drill off the top cap, then use some pliers to turn the remaining top cap bolt.
Look where it got me, there doesn't seem to be any top cap bolt left.


It's a Bianchi Oltre XR4 fork.
1-1/8inch steerer tube. Rim brakes (no hole in steerer tube).

Compression plug was torqued to 6Nm. Top cap was just lightly hand tight.
Compression plug is from Aliexpress and looks like :

enter image description here


I am not planning to reuse the compression plug so it can be destroyed.
Steerer tube can be cut about another 4-5mm.

Seeking your wisdom

I'm not sure if there was actually cross-threading or that the metallic surface somehow fused together (not entirely sure if compression plug is steel or alu).

Please teach me how to remove the whole assembly out of my steerer tube.

Thank you, the Feynmans of the bicycle world!

3 Answers 3


Thanks for all your help!

enter image description here

What worked

Drilling with a small bit into the edges of the broken top cap screw.
Miraculously, I noticed that the screw loosened itself as it's unwinding little by little from the vibration of the drilling.
Then I used some pliers to unwind it out and was able to find a near-perfect hexagon hole where I can stick my 6mm in.


So...the top cap screw thread doesn't seem to be burred or damaged. Even cosmetically it looks fine.
The black anodising on the thread is consistent and no bubbles or cracks can be seen.

But I'm actually really curious, and want to prevent this from happening again!
Please leave your thoughts below so we can learn more from my mistake together.
Did I start the drillium too early? Was there another solution?


  1. Loose headset, and top cap bolt stuck.
  2. T25 top cap bolt stripped.
  3. Araldite in the bolt and on my T25 key, left it over 2 nights, didn't unscrew.
  4. Top cap bolt is aluminium, compression plug bolt is steel.
  5. Drilled off top cap, left an even more stuck top cap bolt in compression plug.
  6. Drilled out top cap bolt, bolt seems perfect.
  7. Please tell me why top cap bolt is even stuck in the first place.

Thanks @Michael and @Carel.
Guess drilling really helped in the end!

  • Did you maybe turn the stem clockwise after setting the bearing preload (i.e. after torquing the top cap to “hand tight”)? This could screw it in further since it’s a single piece design. The same effect could maybe have been used to unscrew it: Turn the stem together with the torx key.
    – Michael
    Mar 12, 2021 at 7:07
  • My bearing wasn't preloaded properly, and I experienced a loose headset. But this is definitely worth pointing out! Will keep this in mind, thanks!
    – Yuxuan
    Mar 14, 2021 at 13:36

Can’t you drill out the top cap screw? It’s aluminium, so should be relatively easy to drill and since you don’t care about the compression plug it doesn’t matter if you aren’t perfectly centered. Just make sure you start centered (i.e. use a centre punch).

Otherwise I guess you could also try to hammer down on the remains of the screw to push it through and open the compression plug. But maybe not really advisable with a carbon tube.

  • I would not 'attack' the thing with a hammer but instead use a screw extractor or have someone who's familiar with the tool, do it. The steerer looks like carbon and take hammering rather badly. And leave the stem in place as it will re-inforce the steerer from around.
    – Carel
    Mar 11, 2021 at 13:14
  • I am planning to drill out a few millimetres of the top cap screw, suffice for my Allen key to have enough purchase to undo the compression plug, then to remove the whole assembly. But how accurate does the drilling have to be in order for the Allen key to have enough purchase?
    – Yuxuan
    Mar 11, 2021 at 14:48
  • 2
    @Yuxuan: Instead of an Allen key, use a torxx key, it's kind of sharper and gets a better grip. Drill slightly bigger than the 'core' of the key and deeper than the ribs.
    – Carel
    Mar 11, 2021 at 16:29
  • 2
    @carel a torx driver that is one-size too big is even better. I have a pile of cheap duplicates from various things, and literally hammer them into place. They tend to be sacrificial, but still work even on a 10 degree off-angle.
    – Criggie
    Mar 12, 2021 at 6:48


Well done for getting the items out and sharing the progress. Based on your success photos, the topcap is not suitable for the forces placed on it because the ultralight topcap is what broke.

From the Top-cap linked website I read these specs:

Option 1:

  • ABSOLUTEBLACK, Headset top cap, One piece cap and bolt
  • Description Do not fit "exspanding" star nuts
  • Material 7075 aluminium, CNC machined
  • Color Black
  • Weight 4 g

Based on the Aliexpress photo you have an expanding compression-style plug, not a star nut as warned off in the description, so one presumes it should be okay.

What I don't understand is why this top cap is stated to not work with a star nut. This leads me to wonder if the compression plug shares some similarities with a star nut such that this top cap is over-stressed.

A star nut does the same task, and I presume has less movement than the rubbery bumpers of the compression plug. Whether that was the cause or not, hard to say.

Option 2: You got a faulty one - some pre-existing damage to the bolt, or a void, or even bad packaging and transit could have pre-weakened the threads. They're only aluminium, so once bent will not straighten.

Option 3: Assembly problem - anodised aluminium tends to slide quite nicely, but raw aluminium doesn't. Could be the inside of the plug's thread was raw, and the anodising rubbed off while tightening, leaving the two surfaces to bind and gall together. As you add torque, the threads lock up and the aluminium bolt gives way.

And the steel thread is stronger than the aluminium one. Perhaps using assembly lube may have stopped this from happening.

Solution: I'd suggest using a regular top cap and steel bolt. If money's no object, a Titanium one has weight-weenie credentials twice over (weight off your bike and off your wallet :-\

  • I know this is not a direct answer, but can't format in a comment and this is too long for a comment anyway.
    – Criggie
    Mar 12, 2021 at 6:46
  • 2
    OP’s compression plug is of the type which should be firmly in place once it’s been tightened with a 6mm hex key. In any case, once the stem is tightened/clamped there shouldn’t be any load on the top cap and you should even be able to remove it completely.
    – Michael
    Mar 12, 2021 at 7:04
  • 1
    I interpret ""exspanding" star nuts" as poor English for "expanding compression plugs". I'm not aware of any expanding star fangled nuts; the OP's top cap is indeed not to be used with the compression plug.
    – Armand
    Mar 12, 2021 at 7:55
  • 1
    Thanks for the insights! I thought about the "expanding" star nut and I realised that it refers to the type of compression plug I'm using. From absoluteBlack(aB) absoluteblack.cc/top-cap.html], they recommended using ENVE's compression plug, which does not feature a steel coil spring. My take is that this type of one-piece top cap should not be used with the generic type of compression plug. There also could be misalignment of the thread's pitch due to installation error or manufacturing. Perhaps the softer aluminium micro-buckled in the harder steel compression plug thread.
    – Yuxuan
    Mar 14, 2021 at 13:52

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