Bottle Cage Allen screw Size

[CoBikeJunkie]

The bottle cage mounts are conveniently the same size/thread pitch as cleat bolts.  If you happen to ride clipless it's super easy to replace a bottle cage bolt with a cleat bolt, then you always have an extra.  It will be at the most inconvenient time if you lose cleat bolt.

[canalligators]

10-32 machine screws can often sub for M5x.8 in a pinch, but they are just a hair smaller and thus run the danger of stripping out. ...

Don't do it!  Rivet nuts in frames are often aluminum and that will be the part that strips, not the screw! 

You can buy metric fasteners at many home stores these days, i.e. Lowes or Home Depot. Or order stainless online.  McMaster-Carr has a bag (of 50) M5x0.8 button head stainless screws (#94500A231) for $7.44 plus shipping.  But non-stainless of the right size is better than trying to make inch size fit.

[WisdomUfot]

I know the thread is old but I just wanna add that when it comes to the bottle cage Allen screws, it's important to find the right size for a secure fit. While it's common for bikes to use standard sizes like M5 or M6, it's best to check the specific requirements for your bike model. You can refer to the manufacturer's documentation or reach out to their customer support for guidance. If you're looking for metric Allen screws, you can try visiting a local hardware store or check out online retailers like https://www.scrooz.com.au/. They offer a wide range of fasteners and can provide you with the appropriate size for your bottle cage installation.

[mobilemail]

I have come to despise these 5mm screws with a 3mm hex key head, they strip too easily if overtightened or not greased.  4mm hex key heads are far more reliable.

[canalligators]

I have come to despise these 5mm screws with a 3mm hex key head, they strip too easily if overtightened or not greased.  4mm hex key heads are far more reliable.

So don’t overtighten them.  Sure, 4mm is better, but you can practice your hand to not overtighten.  Or use a small torque wrench.

One other note on stainless: don’t use stainless screws/bolts for high torque applications, such as boom clamps or seatpost bolts.  Most common grades of stainless have about 2/3 of the tensile strength of regular carbon steel.  You risk snapping off the bolt.