I used to call these Toques.
They're caps that allow your brake hose (or cable and housing) to exit the steerer at a hopefully safer angle than some other options.
I first called them "Hoser Caps", but really, that's a Toque, Eh?
I enjoy methodology and machining;
I could care less* about marketing.
When installed, the part that you see is actually somewhat unnecessary
(I'll explain how to make your own)
it's what's under the Toque that makes it work.
This is the video of how it was done:
If you're interested, the following is why it was done. I'll include explanations of some of the decisions.
This started with the combination of some of the local Polo players getting new frames, a season lost to a pandemic, a looming off-season, some thinking, and time.
The first idea suggested was using a starnut with a hollow bolt and running the hose through the steerer like in old school BMX applications.
Because the requester was going to be purchasing a hydraulic brake with a braided steel line there was the concern that the diameter of the hole in the typical BMX top cap bolt would be too narrow.
The good news is that, say company H, had recently changed to a smaller O.D. brake hose, the bad news of course is that the fittings were still the same and would
blah blah blah.
I suggested the OneUp EDC top cap, we even have the go/no-go gauge, the tap and the guide in the day-job shop.
Concerns about threading the steerer were brought up.
The idea of just breaking a leaf or two out of a star-nut was considered.
I left it with "let me think about it".
I have to stop doing that.
A test piece was made quickly as a proof of concept:
A couple of days later I had made a cap, intentionally leaving one design flaw*:
Then I handed over the proof-of-concept assembly with a section of brake housing and a steerer tube to get feedback.
The feedback came in:
Slot the exit to allow the cap to be removed from the hose - I was waiting for that one.
Lower the stack height of the cap
Enlarge to hole in the plug and make it more of a slot
Offset the setscrew to allow access with the main bolt installed
Loosen the tolerances on the plug
One of the Polo people is left-handed
Now I was all-in; I actually got really good design feedback. Things like a keying system were discussed.
The design didn't change much other than to incorporate the suggestions.
*if you decide to leave a design flaw in a proof of concept and none of your test group picks up on it:
get a better test group.
If you have a different solution to the plug shown but want a cap,
just cut a slot in a headset-spacer and use your regular top cap,
the Toque only has one advantage.
The ledge in the Toque is designed to reduce the chances of over-tightening the pre-load and damaging the hose.
While this design seems to have the advantage of being able to be completely removed without disconnecting the brake,
the brake hose is still captive in the steerer and stem.
I've included a poor quality drawing of the parts if you want to make them yourself or have someone else make them.
A machine shop may insist that you present a reasonable quality drawing.
I specified all dimensions in Metric, because
"Bikes are Metric".
If you find a shop that gets the joke about the dimensions specified,
- particularly the one expressed to two decimal places -
that's a good sign.
As for the dimensions of "?" and "whatever":
This will depend on the I.D. of your steerer and what the shop has handy.
This is the latest Hoser Cap, I still wasn't sold on Toque either...
Then another vote came in for Hoser Cap.
This is the test piece with most of the issues corrected.
This is the first fifth of something that I have made.
I was promised that this project would be limited to a maximum of four requests.
* Yes I meant "I could care less" and not "I couldn't care less". In this case I find that I could actually care less about marketing; if I tried. Am I actually caring less, if I made an effort to care less than I already do?