How to Fix a Loose Water Bottle Boss at Home, and How To Remove a Snapped Bolt

So here's a common scenario: you go to clean behind your bottle cage after a long season of riding and you notice the fixture that holds the bottle cage to the frame is loose, and spinning around with the bolt!

You've already used a needle nose pliers to hold the fixture (henceforth called by its technical name, a 'boss') so that you could remove the bolt, which you intelligently greased at the beginning of the season just in case something like this happened.

But now the boss is still loose, jiggling around. What do you do?

Not to worry, there's an easy fix.

Things you'll need:

Longish M5 bolt made of hardened steel. The water bottle bolt your bike comes with is not made of hardened steel and is easy to break, as we will see later in the post. 

M6 nut. This is just a little bigger than the M5 bolt and will slip right over it, but it should still rest against the boss when the M5 is screwed in. 

A quality 4mm hex wrench with some decent leverage

A 10mm box wrench

Place the M6 nut over the M5 bolt and thread the M5 bolt into the loose boss by hand. If the boss is really loose, you might need to hold it with pliers. Make certain the M5 bolt is covered with light grease.

Hold the M6 nut with the 10mm box wrench and tighten the M5 bolt with your hex wrench.

What's going on is that the bottle boss is designed with a "crunch zone" between the face of the boss and the threads. You can see in the picture below that there are little lines on the outside of the boss. That's where it bulges out. When it does that, it squeezes against the frame, jamming itself in place.

You might have to put a lot of grip into getting the boss to bulge firmly against the frame. This is why you want to use a high-quality bolt. A crappy bolt can strip, or in this case, break:

Luckily, removing a broken bolt is easy. Because the head broke off, there's nothing creating back-pressure to keep the bolt in place. Also, since we greased it, there isn't much friction getting in the way either. The bolt remnant should twist right out with the help of a pick or sharp screwdriver:

Once the bolt is out a little bit you can help it the rest of the way with pliers:

Now what if you used the correct hardened steel bolt and you got the boss as tight against the frame as you possibly could, and it's still spinning? Well, you might just have a bad boss. But who doesn't? Har har har.

To replace a boss, it's best to bring out the big weapons. This is a rivnut gun:

It works the same way as the M5 bolt and M5 nut trick, but with more power. It's best to start with a new boss too, so you'll want to drill out the old one, then remove the seat post to shake out the little bits that broke apart while drilling.

Once the boss is firmly in place, you can screw in a water bottle cage with it and never worry again.