I’ve mentioned the small plastic cap that Bromptons ship in this post: It goes over one of the front wheel nuts, and helps to protect the bike’s finish when folded. Mine developed a crack almost immediately after Basil arrived. Perhaps that wasn’t surprising; this particular fitting may never have been intended to remain on a Brompton, once unpacked and in use.

Once the crack enlarged, and before the cap could fall off, I removed it and took off for the hardware stores. In my many hours of haunting the small bins there, I knew I’d seen something that would do the trick. I found it:

It’s a nylon “hole plug locking”, size 13/16ths, extortionately priced at something around a US dollar. And well worth it, as far as I was concerned. (Why do I suspect that the packing was more expensive than the bit within?)
The replacement cap has an arguably better design than the Brompton original; instead of a somewhat radically curved edge, the edge on the replacement curves slightly, but has slots to relieve, and then retain, pressure, which I would expect to hold up better than my poor split, unperforated, original. The new cap required a bit of contortion during installation, but has stayed firmly in place since.

Whilst on a group ride yesterday, I showed this to Mike, of Trophy Bikes in Philadelphia. He was quite interested, and I was amused by his immediate question: “Does it come in black?”
Yes, I believe that it can be found in black, though your mileage many vary — along with your eagerness to canvass every hardware store in town. I like the white; I’ll notice if it goes missing.
Nicks and dings are inevitable — and, certainly, indicative of a proud history — but I’m just as happy to postpone them as long as reasonably possible.