Yesterday when we were putting a new rear derailleur on Kuroko we discovered that some of the screws for the modular dropout were missing — in fact, most of them were missing. And from the looks of the recesses in the frame, one of them has been missing at least since my ride in England.

I hadn’t paid enough attention to the dropouts before to realize they were modular, much less that they were held in by screws. A quick inspection showed that the other side was fine: all present and accounted for, and nice and snug. On the drive side, just one screw remaining, and holding in by a single thread. It has me wondering if this contributed to the earlier issue of the thru axle coming loose on a regular basis. And I’m sure a wiggly dropout would contribute to sloppy shifting.

Regardless, it would be unsafe to ride Kuroko in this condition. I needed replacements. I tried searching online for information, but nothing was forthcoming. So today I took the remaining screw and set out for the bike store. The clerk there was able to find something similar for me, but he was concerned the head shape was different and wouldn’t sell it to me.

Instead I went to Tokyu Hands and bought screws in three similar sizes, thinking that one would be a sure winner. Amusingly, the three varieties of screws at Tokyu Hands (not known for its bargain prices) cost pretty much the same as the one screw at the bike store.

The first screw type I tried was a pretty good fit. Not perfect: the head is a bit round and stands out just slightly from the frame surface. But I think it’s good enough. If there’s a clearance issue I’ll cut down the 16mm screws to fit as they’ve got flat heads. Meanwhile, I put Loctite on the screws and tightened them up.

So who’s to blame?

Obviously having a dropout fall off while I’m on a ride is a safety issue. I’m lucky it didn’t happen on one of the English canal paths or halfway around the Tour de Tohoku. How could this have come to pass?

I don’t really know where the blame lies. There’s not really a good reason to use a modular dropout on a production frame unless you use the same frame for a variety of models, some with thru axles and some with quick release. But given that’s what we have here, were the screws driven in by the maker or the bike shop that assembled it for me? I don’t know for certain, but I’m guessing the maker.

The final possibility is that I damaged the screws when I had the derailleur go into the spokes on that fateful day in England. I can’t completely rule that out. I do know that I was having the issue with the thru axle loosening up before that time.

Regardless of where the finger points, I now have something to add to my pre-ride checklist, and it probably wouldn’t hurt to carry spares on longer rides (particularly given they weigh next to nothing).