I just brought home an aluminum frame Univega road bike . It has mounts for 2 bottle cages .The bolts for both are frozen in the frame . There is some kind of insert in the aluminum that is threaded that the bolts screw into. When trying to remove the bolt the insert just rotates in the aluminum tube.

Any idea how I can get the bolts out?
I thought of trying to drill the bolt out but that would probably just ruin the threads of the insert.

Could I drill out the insert too? If so can I get new inserts?

"Rivnut" threaded inserts are typically used as bottle mounts on aluminum frames. You may need to pull the whole thing out and replace it with a new Rivnut. Many bike shops have the tools needed to do this. Take care to lubricate the bolt threads when you install your bottle holder so they don't seize again.

This has been covered many times here, loose RivNuts. First step is to understand fully the situation and then try non destructive methods before pulling out power tools. What is the access to the tubes' insides? The seat tube is a no brainer but what about the DT? If you do drill out the RivNuts the inner portion will fall into the tube. Will it sit there for ever being a source for rattles or can it be fished out via a vent hole? Have you tried to soak a penetrant into the frozen fittings yet? Using a tiny screwdriver's end pushed under the RivNut's lip can sometimes keep the RivNut from turning while the bolt is loosened. Drilling the fitting out will take some focus and care. You have a fairly hard bolt (and likely stainless steel, not that the material didn't become corroded corrode in place) and a fairly soft RivNut as well as frame. Patience is your friend. Andy

fwiw ~ you can leave them alone & mount bottle cages with other methods

Two things to add to Andy's suggestions:

You can try to put a few drops of gap-filling retaining compound (commonly sold as a 'green' threadlocker) or thick superglue (available from hobby shops) between the gap, and wick it in by spinning the insert. After it cures, it may be enough hold to allow you to remove the screw, and properly re-set the rivnut.

Maybe try to heat the bolts up a little with a blow dryer or a heat gun if the bolts have a strong loctite on them. If they just won't budge, removing and replacing the rivnuts is not too difficult. I made a video a year or so ago showing the process.

Thanks people,

I will try some of your suggestions.

This is a bike that the Bike Exchange will be selling. If I have to leave everything be - oh well.

On the other hand I would like to make things right.

Also a good teaching moment for this 71 yr old semi pro bike fixer.

Gorilla Glue might work. It foams up and fills gaps, and sticks to a lot of different materials. A very small drop, about the size of a match head, will be plenty. I seem to always use too much. I'd use masking tape or scotch tape to protect the paint near the rivnut.

It's useful for a lot of unusual gluing jobs. For example, I glued the plastic clip in place on my saddle bag that holds the end of the strap. Green threadlocker is quite specialized, and you may never use up the rest of it.