This is frustrating me. I recently bought Shimano Dura Ace ST-R9120 hydraulic levers/BR-R9170 calipers combination. Got to the stage of bleeding the brakes and removing the bleed caps from the tops of the levers. The caps, as tensioned from the factory, will not undo with a new hex key fully inserted in them. Instead the key takes some tension and then spins around in the hole without moving the caps. To remove the caps I had to get a large set of vice grip pliers and start the caps turning. Of course in soft aluminium that means the outside of the caps are now marked. A pair of these is now on the shopping list:

enter image description here

You might imaging this is using a ball-end key or the wrong size key. No, this is using a new metric set, fresh and unrounded. Nor is it undersized, same as every other key or socket I can find.

Same situation with various other Shimano bolts. Though larger bolts will not let the wrench spin in the socket and fail to move they will grab the wrench when tightened to torque as if the bolt head is deforming and requires some backward movement to release the wrench. Not using too much torque - in fact using a torque wrench to specification.

What is up with their bolts? Am I supposed to buy Shimano 2.55mm hex keys or something here? Are they just using hex driver sizes inappropriate to the bolts? Maybe hex is just bad at transmitting torque and we should be using square (Robertson) drivers.

  • That's ST-R9120 on your photo, not ST-R9170! ST-R9170 bleeding port is located at the middle of bracket, right above Di2 guts recess. I'll check my ST-R9120 bleeding port bolt tightness and report later. Dec 17, 2018 at 2:20
  • Well spotted - I pinched the photo but it is the same as my lever. Their numbers confuse me - I have 9170 calipers, 9120 levers. Will update question. Dec 17, 2018 at 2:22
  • Have you considered buying better quality wrenches? I've noted considerable difference between wrench brands when it comes to fit. Dec 17, 2018 at 2:37
  • 1
    This sounds like a quality control issue. Have you contacted the seller? Also, the spare part costs 3 pounds, in this situation I would just buy new screws and see if they have the same issue.
    – ojs
    Dec 17, 2018 at 7:22
  • 2
    I will definitely be buying new screws, but the ones that were in the levers were too tight as supplied - no way to unscrew without marking them up. Filing a flat screwdriver slot before insertion seems like a good idea. Dec 17, 2018 at 21:24

2 Answers 2


Well, it's not just you, my ST-R9120 bleed screw accepts 2mm (as stated in manual) very loosely too, 2.5mm is too thick, there's even a whole thread on WW dedicated to the issue, apparently those screws are/were of very poor quality, this was not the case with ST-RS685. Some of proposed "solutions" are:

  1. Hammer T10 in. Now you have a T10 screw, but this still might not help or even damage the threads.
  2. Or file a flat screwdriver slot and use it instead.
  3. Contact Shimano for a warranty.
  4. Buy replacement screw(s) (Y0C698030).
  5. Try to push hex key further, some people stripped the slot by not pushing the key deep enough.
  6. File a 2.5mm hex key down so it fits tightly.

Update: among three sets of hex wrenches I have access to, one had 2.5mm tight enough not to strip the bolt. Both bolts unscrewed with a slight click. So, #6 worked for me.

  • 1
    Just to note, I'm going to try #6. Dec 17, 2018 at 14:32
  • Bummer, and are they actually aluminum in addition to being sized badly? Dec 17, 2018 at 18:18
  • THANK YOU! Nice to know I am not the only one, I hate stripping a bolt. @NathanKnutson - yes, they are a very soft aluminium. Dec 17, 2018 at 21:26
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    FWIW, another remedy I've heard of, for dealing with hex keys just a little too small for their sockets, is to put the key in a vise, tip up, and whack the tip with a hammer to bulge it out (technically, upset-forge it).
    – Adam Rice
    Dec 17, 2018 at 22:23
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    Another option when you can't get access to file (or dremel) a slot is to drill a pair of holes for a "snake-eyes" security bit. Also you could glue (epoxy) a 2mm bit in, let it set, then get the screw out. That sacrifices the screw and the bit so have spares on hand
    – Chris H
    Dec 18, 2018 at 7:32

Im having same problem.You can try a 3/32 imperial hex key mine measured 2.36mm though it hasnt worked in my case.2mm is too loose of course and the 2.36 i cant even tap it in.So anyway just thought id mention this could save some of the filing down as its closer to the size i need.My only other suggestion is center punch around the edge very carefully may shock it loose.Also will need a new bleed screw after that.Thanks for the other suggestions all worth a go.Im so annoyed at this point i want to take the lever off and beat it with a hammer until dead.

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