Trouble installing Bluetooth sensor
 

This past Thursday, I bought a new Trek FX2. At the same time I bought a wireless computer for it, and while the store offered to install it, I was a little pressed for time and told them I could do it myself.
Two screws for attaching the sensor were supplied. An 8mm long for alloy frame bikes and a 6mm long for carbon frame bikes. The instructions make no mention of screw size and pitch. I’m not too familiar with metric screws, but I’m guessing the screws supplied were size m3. When I couldn't get the 8mm screw to start I removed the sensor to see what the problem was. The screw supplied with the sensor literally falls into the hole it is intended for. Like trying to screw a 6-32 into an 8-32 hole. I went to the local hardware store and got a size m4. I couldn't get it to start either. At that point, I called the shop where I’d bought it. The guy I talked to was really puzzled about the problem and said he would get back to me. Maybe fifteen minutes later, he called back, said he’d spoken to Trek, and that I needed an 8mm screw. As already established by the directions, that is the length, not the size.
In the hope that paint in the threads is preventing the m4 from starting, I am going to try to find a m4x70 tap later today. If paint is the only problem it should chase out without too much trouble.
The thing is though, although the mechanic at the shop has not run into the problem before, a little internet searching indicates that it isn't unique. Has Trek slipped on their QC to the point that what should be standard screw sizes in braze-ons is not necessarily “standard” anymore?
I have definitely reached the point where I wish I'd let the shop install the sensor. However, due to distance, that is a last resort at this point.
I plan on installing racks on this bike at some point in time. Hopefully it won't be as much trouble.

Yet it sounds like the best option for you at this time.

Yes and no.
Round trip driving time to the shop is close to three hours. Working in maintenance for years, along with a spattering of gun work, has trained me in the task of using taps from from 4-40 up. The main purpose of my post was how a bike can leave the factory with a hole drilled and tapped (at least I guess it's tapped) for a screw that is larger than it should be.

Egg on my face.
I looked at the problem this morning and saw what I was doing wrong. '''Twas a classic case of cranialrectumitis.

Was alcohol involved? 8-o

No.
Just a matter of doing something I don't normally do and not being able to see the obvious.