Sourcing GRX Caliper bolts - Y8N204000

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  • Long story short I've bought a GRX groupset from eBay and belatedly clocked that the mounting bolts are absent. I figured they would be easily sourced.

    However having figured out exactly what would be needed for the frameset I can't seem to find the necessary bolts for the front caliper. SJS have the rear bolts in stock but not the front, and not til July either.

    Any thoughts on where they can be sourced, or do you happen to have a spare set that you're willing to part with please shout?? Equally is there a non Shimano work around? Cheers.

  • Do you need the ones that hold the adpater to the fork or the caliper to the adapter?

    Caliper to adapter are something like m5 x 12 or 15mm counter sunks, adapter to fork are also m5 I think but a bit longer (20mm?) and dome head will work best to clear the caliper.

  • I need the one to fix the adapter to the fork. Looks like they are 17mm going by the SJS page.

    https://www.sjscycles.co.uk/brakes/shima­no-brrs505-caliper-fixing-bolt-a-y8n2040­00/

  • From the reply to one of the questions?

    That sounds more like an m5 x 12.5mm with a 4.5mm deep head. Which is what the photo looks like, but with sram calipers at least you need something with a lower profile head to allow the caliper it’s full range of movement.

  • This photo of a grx front brake definitely looks like it’s fitted with a bolt with a shallower head than the one in the photo on that sjs link.

    Lengthwise, what is the rule of thumb? The diameter of the bolt is the minimum engagement you should have so as long as there’s more than 5mm projecting out of the adapter it should be ok?

    Edit: that’s where the female thread is of the same material/strength as the bolt. The thread in the fork will likely be aluminium not steel so... double it? 10mm minimum engagement?


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  • I think that's maybe just a trick of the light and the washer in the SJS photo?

    The frame manufacturer have advised me that the linked bolt is what's needed. Probably don't want to go off spec for such a key component.

    Anyone else have any ideas, or got a couple sitting in a drawer?


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  • Yeah could be right, the photo on sjs looks like a deeper head but can see it’s actually just a gap between the bolt head and washer.

    A standard m5 cap head bolt will probably have a deeper head and could foul the caliper so I’d still suggest a dome head bolt.

    Thinking about it, the 12.5mm measurement quoted on sjs probably means a thread length of 13mm with the washer taking up .5mm.

    On the other hand though, from a quick search it looks like standard lengths are 12mm and then 16mm. Stick something down the hole, see if there’s room for 16mm, if not, get the 12mm?

    You’ll get about 50 of them on eBay for the cost of that single bolt from sjs.

  • Just hit up a bike shop. They should have some sitting around if they don’t recycle everything. We have a whole bunch of spares of them at work.

  • Just use a pair of M5 bolts, the sort you get with every other disc brake, chop to size if too long. If the bigger head fouls the calliper search for that specific bolt

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Sourcing GRX Caliper bolts - Y8N204000

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