Not sure how safe but it appears this is intended to convert 1 1/8 t 1" Headtube https://www.ebay.com/itm/1-1-8-to-1-...sAAOSwF1dUR0Zf

I would think they're safe, since everything's "clamped" together. How well they work is another question. If you chase and face the head tube properly, and these things press in, then you'd be pressing in the cups on something already pressed in. Off-concentricity from tolerance stack-up might make for a less than ideal headset adjustment, but then, a lot of production bikes were built with poorly faced and chased head tubes, and they're rideable.

Okay, I think I have a solution: Bilenky Cycle Works in Philadelphia can braze on a new threaded steerer in place of the original threadless one for $125, which strikes me as very reasonable. The new steerer will have rolled threads. More about that in a moment. I assume that the powder coat on the fork crown and surrounding area will be toast after the work is done. It wouldn't be hard to have the whole fork refinished--there's a powder coat outfit near me that seems to do excellent work on bike frames--but knowing me I won't bother. I specialize in cosmetically imperfect bikes.

The Yellow Jersey shop in Madison would be willing to thread my threadless steerer for $60 per centimeter. Figuring a headset with a 40mm stack height, that's in the neighborhood of $250. Steerer replacement wins big in terms of cost, compared to cutting threads.

Also, based on my correspondence with Steve at Bilenky and Andrew at Yellow Jersey, I gleaned the following information, although it's still not as definitive as I would like it to be.

Andrew seems to say that cut threads are indeed smaller than rolled threads, and don't engage as well with the headset threading:

"I have filled in cut thread and recut where the material was intended for rolling or AH [not sure what AH is JV] and the cut thread engagement was poor. On our fine-thread bicycle formats, a few thousandths matters.

If it were a one inch I'd be more positive about it. It's a better design and we have better piloted tooling.
For 1-1/8x26 the format is ridiculously fine thread for the diameter and tooling isn't quite as positive for new thread centering.
The threadless column material is on the small side for a perfect cut thread. A good caliper and two forks will show that."

I guess all that makes sense. Rolled threads on spokes--which is the rolled thread that I think most of us are familar with--are obviously larger in diameter than the spoke itself. But the fine threads on a threaded steerer are so small in proportion to its 1" or 1 1/8" diameter that it's probably not easy to measure (hence Andrew's comment about a few thousandths mattering.) It would mostly be reflected in a somewhat sloppier fit of the headset parts.

In practice that might not matter much. If threading the threadless steerer was a lot cheaper, I might be tempted to take that route. But since a new steerer with rolled threads (per Steve at Bilenky) is half the price and gives a better end result, that seems like the obvious way to go.

I don't get why 1 1/8" standard decided to go with 26 tpi rather than the 24 tpi used for 1" and french. Are you going to have a 1 1/8 steerer brazed on and deal with the limited headset/stem options or go with a 1" steerer and use headtube shims to get a wider variety of headset/stem options?

I agree that the new steerer seems to be the way to go. Even with powdercoating the fork, it would probably come out cheaper.

Cool. For $125 the new steerer is the way to go. Problem solved! I'd probably rattlecan the fork myself. Surly's are supposed to be utilitarian anyway, I think.

I checked and 1 1/8" threaded headsets are still pretty easy to come by. Ritchey sells one for ~ $15, or splurge on a Chris King for 10x that. There's a Tange in between.

I love happy endings! Pics will of course be demanded.

Holy smokes!

French thread steerer pitch is 1mm or 25.4 tpi.

Who knows why, but the BSC spec for 1⅛ was 26tpi and has been since 1949. It was used on tandem steerer tubes long before mountain bikes picked up the size. The reason I would guess is that a finer thread removes less material from the tube, so the threaded section stays stronger. That's probably more important on a tandem headset that has to carry twice the rider load on only a slightly larger diameter tube.