My road bike has a carbon frame with brass bottle cage inserts. In attempting to drill out a snapped bottle cage bolt I mangled the insert which I then dropped into the frame when trying to remove it. The carbon is undamaged.

Can you get replacement bottle cage boss inserts?

EDIT just googled – will a riv-nut do it?

Rather than a riv nut I would look to using a helicoil thread repair. You only need to drill out the thread, and put a larger tap (specific to helicoil repair kits) and not too much more where a riv nut may need a bigger hole which would be scary in a carbon frame. Also if the riv nut starts to spin in the hole you are knackered.
A helicoil will leave the thread stronger than the original, will not spin in the whole once you have used it a few times and you can bask in the glow of doing a proper engineery fix.

The entire insert is already gone, leaving a fairl large diameter hole in thin carbon. I don’t think there’s enough material there to use a helicoil thingy.

As for rivnuts spinning – that seems to be fairly common on my bikes 🙁 Good glue is required.

They would have been brass-plated rivnuts to start with, probably.

Now you have a hole in the frame, why don’t you just fill it with water and attach a long camelbak hose. Streamline is all the rage.

rivnut + a washer bent to match the shape of the tube + use some glue when fitting …

never had much success just fitting a rivnut on its own……

stainless washer not ali as the rivnut will pull it flat and it will look horrible……

Like the camelbak idea.

Any particular type or brand of rivnut?

The top of the tube is flat, so no bending required – that’s handy I suppose 🙂

Original seemed to be brass in colour and fairly soft, but who knows what it was made of. I’ll see if I can get a tiny magnet to fish it out of the frame.. doens’t seem to be rattling thouhg, pehrpas I’ll just squirt some glue in there to be sure 🙂

Sorry for mis reading the OP Molgrips. It does sound like the riv nut is the only option. Though I also like the camelback idea.

simple, use a Rivnut

we regularly repair frames (sometimes on brand new bikes) where the original rivnut fitting has become damaged, or was not installed properly to start with

the gun we use is Emhart Technologies “Pop Nut PNT 110” and the rivnuts are standard M5 steel

entry point for reverb stealth?

You have to have this expensive gun to do these?

M5 bolt a couple of washers and a nut will do it.Or you can use a qr and a lot of spacers instead.

If you want to help the rivnut seat well, epoxy it into place to provide a larger stress relieving area. You don’t necessarily need the pukka tool, a suitable long threaded bolt with a nut and a couple of washers on it (well lube’d) will compress the nut fine. If this is your first time (pfnaar), then buy a couple of nuts and practise on a spare bit of something you don’t mind about to get the hand of knowing when to stop tightening!)

a suitable long threaded bolt with a nut and a couple of washers on it (well lube’d) will compress the nut fine.

Ok excuse my ignorance.. but wouldn’t that require access from the other side? Or will it become obvious when I see how they work?

I could just epoxy the thing in place tbh, couldn’t I? It’s carbon, should bond well.

Long bolt, yes, nut, no – you want the bolt to be able to pull up on the rivnut to flare it out.

However I doubt you’ll get as much force this way as you would with a proper tool – it might not flare properly.

frankly, on a thin walled carbon tube I’d be looking to a) use the right tool and b) get someone who’d used the right tool before to do it.

Any frame builders local to you?

I don’t understand how you remove the bolt after you’re done flaring…?