M7 bolt for Bontrager seatpost clamp

I’ve googled this post’s title quite a lot since I snapped off my saddle last week on the way home from work. It turns out that Bontrager like to use very odd sizes of bolts that you local bike shop is unlikely to stock. In fact most people I spoke to were of the opinion I’d have to buy a whole new seatpost. Not so.

After some hunting I settled on a 50mm M7 socket capscrew bolt from Stig’s Stainless Fasteners. I hope this saves someone some time.

62 thoughts on “M7 bolt for Bontrager seatpost clamp

  1. Thanks for this… same thing happened to me earlier this week. Any idea what the name of the bolt this screws in to is called? Must’ve left mine by the side of the road somewhere.

  2. Exactly the same thing has just happened to me. Thanks for the tip on where to find a new bolt but I’m wondering if the M7 is inherently too weak given that we have all had them snap from under us? Might be a better idea to get something more substantial?

    1. M7 is just the size, I think perhaps its the quality of the default bolt. I’ve done another couple of thousand miles since then and had no problems.

  3. Thanks man, you just saved me a good few quid. Fits like a glove and was delivered in a couple days.

  4. This blog post has brightened up my M7 boltless day 🙂 Saved me lots of time after the same thing happened to me

  5. Life-saver. I had this exact problem and this was one of the first results google came up with. Now I know what to ask for at my local hardware shop.

  6. Just snapped my cap screw today. That looks exactly the same as my seat clamp assembly. You’re not kidding about bontrager using odd sizes. Cannot find an M7 here in the states. Plently of M6 and M8’s. Im curious, did you have to saw the end off??? I saw something that said it was 45mm long. Im off to Scheels tomorrow where I bought my Trek.

  7. Same thing happened to me – my Bontrager saddle on my Trek snapped resulting in a back splat on a busy road and a busted elbow. Just ordered my M7 replacement but worried about getting it on – if the bolt size is unusual then maybe i won’t have the right tool to put it on!?

  8. When mine went I simply drilled out and tapped the hole to standard M8. Sorted, and bolts available anywhere. Been good for a year now.

  9. Haha, in Holland i was tryin to find it, but don’t waste your time, impossible. All bike shops just lookin and like one says, noah, sry, we haven’t.. The same for me, thank u for this.. 🙂

  10. Thanks – just ordered two. Unfortunately I had already spoken to two bike shops and the second one who is normally very good I bought a new seat post from!!!! So now with bolts in place I will have a spare ready to go if I ever have the need.

  11. You sir, are a legend. I spent most of yesterday trying to find a replacement bolt, and even my local old school, “fork ‘andles” hardware shop couldn’t help, and they stock everything.

    Particularly annoyingly, this seems to be a known issue which prompted a recall in the states but neither Trek retailer I visited yesterday could help – http://www.trekbikes.com/pdf/recalls/56789.pdf

  12. Thanks a lot Andy. I had the same problem… snapped it while riding back home from work. I just ordered mine from Stig’s.

  13. Wow… i was just giving up hope .. ebay then a web search .. no joy. i wondered why on earth use these size bolts!!! just spoke to stig and he is sending it out today ..Thankyou so much for this post

  14. Hi we’ll some 4 years since first posting and people still having the problem this has happened to my wife on the way home luckily she was not injured and fortunately the bar nut was caught in the cycle lock wire which was coiled under the saddle well some time spent visiting local cycle shops the be surprised not one could supply? For something that a lot of us suffer. I found out the bolt was a caped M7 bolt from one engineering firm but they didn’t stock as it tended to be a specialist size. So from search the good web eventually found your post and have ordered two bolts today hoping not to require the second but one in hand. As some one mentioned a issue of quality I would have said as the bolt I have sheared at the point the thread starts after the shoulder under the head as to someone’s posting in the middle. Thanks for highlighting your supplier I wait to get replacement and replace the current M6 nut and bolt I have used to keep the cycle on the road.

    1. Further to my last comment the bolts arrived two days latter and fitted and all good again a great service from supplier.

  15. Was looking forward to a couple of happy hours scouring the internet for that little baby and you’ve just spoiled my fun. Now I’ve got to do some accounting I was putting off – ruined my evening I can tell you. Thanks anyway. Jonathan. x

  16. Looks like I am the newest member of the ‘elusive M7 sheared-off Trek bike’ club. like most of you, I have spent a couple of days looking for the impossible; an M7 bolt for my Trek 7.5fx saddle which failed 5 miles from home last week. Even a Trek dealer told me I needed an M6 which, obviously, was wrong. Will now order the item from your recommended dealer. Thanks for brightening up my grumpy mood. Steve

  17. Slight problem- the link goes to an inactive website. Does anyone have a direct email address or, preferably, a contact number for Stig that they can share so I can make contact? Cheers Steve

  18. Latest member of Trek splat on the pavement club here! Got away without too much damage – cuts and bruises thankfully. Found this page after visiting Halfords and finding out the bolt’s an unusual size. Ordered from Stig, delivered next day and bike now up and running!

    Thanks so much for the page – v useful!

  19. Thanks happened to me last night luckily I didn’t lose any family jewels or tear myself a new………My dear wife picked me up took me home.
    Then the search took me all places last night B&Q no, Halfords, no, screwfix, no, just did a quick internet search this morning and found this!
    Thank you Andy!
    Just placing order with stigs now. Currently hashed together a m6 cot bolt arrangement and sitting gingerly all the way into work this morning.

    1. Thanks Andy – I’m constantly amazed at people’s generosity and genuine desire to help over the net – you join my list of heroes. I too had been told I’d have to buy a new seat post.

  20. Same for us. Wife’s Bork snapped where thread meets head. Nasty. Tumble and shocked. We scoured hardware shops in France same as other folk 6 or 8 no problem.

    Temporary fix – 7mm thread rod , washers and nuts. That will do for the week but ordered via link for a proper job , after reading the rest of the thread install an order. A new one for. My trek and swap out as a pre-empt.

    Thanks for finding this and people bothering to post to keep this live.shame on trek as this does appear to be a quality issue on. Otherwise brilliant bikes.

  21. Thanks for this – mine snapped off today (2009 Trek FX7.3) as I was riding along. Ordered from Stig and fingers crossed it works!

    1. Hi – following up from my last post – the Stig bolt would only stay tight for minutes before becoming loose. I am not sure why. It didn’t come with a washer and the head was a bit bigger than the original, so perhaps it wasn’t flush. Either way I bought a new seat post (Ritchey Comp 2-Bolt Seatpost – £27) and can now ride without fear of impalement.

  22. Same issue…bolt snapped (thankfully it happened at less than 20kmph as was slowing at lights) and visited all local hardware stores…got a 50mm x 7 but cannot tighten properly so just ordered 2 from Stig…hoping it’ll tighten properly. Great that this info is being kept alive, many thanks!

    1. Terry – get in touch with Trek – they sent me a new seatpost with a modified clamp free of charge. I was in touch with Stephen Parrott (details below) who sorted this out for me last July.



      Stephen Parrott
      Trek Bicycle Corporation Ltd.
      Technical Services
      TEL: +44 (0) 1908 360160
      Registered in England No: 2355933
      Registered Office: 9 Sherbourne Drive, Tilbrook, Milton Keynes, MK7 8HX

  23. Thank you Sir!
    Had the same issue last week, was told in 3 different shops I had to have the seatpost changed
    Found this page, order from Stig, it arrived in 24hours! first class delivery. Totally recommend

  24. Wow. seven year old post and still happening. Thanks for the info. Had assumed it would turn out to be imperial but no imperial size seems to match. Just ordered. In the meantime have used an M6 Barrel Nut from bed spares 🙂

  25. Same happened to me today. I was ridding my Trek 7.4 FX on a path, at slow speed, and suddenly the Bontrager seatpost clamp broke and saddle fell off.

    I managed to get the parts from the ground, and the M7 bolt had snapped.

    I am not specifically overweight, the saddle was not in a weird angle, too forward or backward, and the bolt being vertical does not bear any weight anyway, it’s just keeping the clamp together. Some serious manufacturing issue here, and no advance warning of failure…

  26. Thanks so much for this post and the link to Stig – new one winging its way to me now!
    Quite hurt my behind when it went too…

  27. Came to this website after visiting many a cycle shop with no luck. Ordered two from Stig, great job and saves forking out on a new seat post for the sake of a failed bolt. Thanks.

  28. Man alive. Thank you so much for this. Bought an M8 bolt from Halfords assuming it was the right thing. Of course it wasn’t. Given the number of posts on here maybe we have grounds for a class action against Bontrager.

  29. I had the same problem a week ago with Trek seat bolt snapping. Thanks for this post, ordered 3 m7 bolts yesterday and received today. Bike seat now back on. Thanks again.

  30. Same here. Many thanks for identifying the bolt, and for posting pictures that show what it connects to. So I’m confident that I’ve now ordered the right replacement.

  31. Thanks for this, seems there are a lot of people with the same issue over the years. The bolt on my 7.3fx lasted about 6000+ miles before it disintegrated. I Wish I had searched sooner instead of wasting money on a M8 in halfords and an M5 on amazon. Anyone know what washer would be suitable?

  32. My son broke the bolt on his saddle last week. Googled for ages without success and then found one in China and it finally arrived today but was, of course, wrong. Google again today, not expecting too much and found this thread. Just ordered a pack of four as we have two bikes with the same connection and I assume the problem will occur on bike two at some point. Thanks for pointer. Great stuff!

  33. Thanks all – happened to me on Saturday and luckily I was riding in Central London and not out in the countryside so was able to get home on public transport.

    Didn’t want to buy a whole new seat post!

  34. Hi

    I ordered 3 bolts from Stig Fasteners in 2017 and now that the second one broke I thought of ordering some spares again. I was so happy this post is still up!

    There is a problem with the website which does either not allow delivery to France OR it allows it but adds a 999,1£ delivery charge. Does anyone else have this problem? Or is it the Brexit way? 😀

    Also, I would like to know if anyone else ordering these bolts from Stig Fasteners found that the heads tend to go out of shape so that fastening the bolt with an allen key becomes impossible after a while. Also they might be a very little bit thiner than needed letting the saddle change position quickly even when tightly fastened.

    Since this bolt sizes are impossible to find, I just rode my bike with the saddle comically tilted upwards for the last 3 years.


  35. Thanks for this thread. I could have taken the photo at the top myself. Seems to me the fundamental problem is that Bontrager is using poor quality bolts that keep snapping. It seems to be only a matter of time before injury/death results – and in fact, they probably have already happened since this thread is 10+ years old, but the unfortunate victims haven’t read this. Are any lawyers reading this thread???? [Just spotted Hugh’s comment from 2018 – Yes, I cannot understand why no one has organised us into a class action suit……Lawyers too busy to cycle??]

  36. This is the post that keeps on giving. 15years down the line my bolt snapped. Nice thought googling would give the perfect solution. Felt like I was winning at life.

    1. Haha, the gift that keeps on giving. Failed to find a replacement bolt at local bike shops then decided to replace seat post myself which is seized.. hopefully this does the trick for under £5 all in rather than a lot more. Thanks again

  37. Wow, so I’ve just come across this thread after searching around many Dutch bike shops all morning for this M7 screw. Unfortunately I wasn’t so lucky with my bolt breaking. I spent a Saturday in hospital a few weeks ago after falling directly onto my back. I was going about 40kmh downhill, luckily someone was behind me that called me an ambulance, and even more lucky that the x-ray showed no fractures, but I still have pretty bad back pain. Could’ve been worse but it’s not good at all that Bontranger have been using such bad quality screws.

  38. Well. This post is still coming in handy. Within spitting distance of home here in Singapore after a long ride and went over the speed bump outside the condo and snap. Thanks for the info!

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