A long time ago, I almost bought a circa 1970 Cilo. It had a similar stay cap treatment though I don't recall if it had the 3 holes in the lugs. The only other thing that I recall is the reason I didn't buy it. The fixed cup was marked 35 x 1G (Swiss thread), the BB was extremely rough and there was too much difficulty in sourcing Swiss threaded Campagnolo cups at the time.

Those 3 holes on the lugs were popular once; I have them on my 1978 Trek TX 900.

I bought a rough Cilo like that; someone had destroyed the threads. I had it tapped and reamed to Italian which fixed the problem.

But a 3 digit serial number tells me it's probably not a mass produced frame. But I'm no expert.

Oh yeah, I'm not claiming it's a high end Trek, it's not. The 3 holes were just a nice touch that you saw on different high end bikes back in the day.

We'll have a better idea of what this might be once the OP tells us the BB and HS threading. Looks like it should be Italian but one good measurement is worth a 1000 guesses.

is the fork crown an Emilio Bozzi product? I know I've seen it before but can't find an example in the usual suspects (Velobase, Velo-pages, CR) it's definitely an Italian (or Italo-popular) brand.

He measured the BB shell width at just under 68mm, and I assume he's seen Sheldon Brown's bottom bracket crib sheet. I'm itching to see what the BB thread and seat post clues are!

This evening, I did all the measurements that I think will provide clues to this frame's origin. Unfortunately, I'll have to wait on the BB threads - I couldn't find the BB I was going to use to check it with. But here is what I did measure:

Frame size: 55cm (Exactly my size! How cool is that?)

The BB shell measures 66.1mm across - strange, that.

Seat tube: ID = 27.2 OD = 28.7mm

Head tube OD: 31.8mm

Top Tube OD: 25.5mm

Down Tube OD: 28.7mm

Rear spacing: 120mm

FORK

Steerer Tube: ID = 22.2mm OD = 25.5mm

Fork Spacing: 103mm

The only other item of interest, since I didn't have my camera out there tonight, is that the 352 is also stamped into the bottom bracket - with the same double-strike that we see on the steerer tube. Another strange attribute. I've reached out to Brent Steelman to bring this frame to his attention, and see if he made it - still waiting for an answer.

no way that Brent made this frame, not even in a previous life (well, we will never know THAT)...in fact I thought this was an April Fool's prank to even suggest it.
That aside, the measurements kind of cloud things up rather than shed light (for me, anyway): it's seemingly more likely Brit (or perhaps Benelux) than Italian, but the BB threading is even more important. A 66.1 shell width may indicate that this shell has been "faced" with a heavy hand. One thing NOT in question: it's a really nice frame!

Why specifically did you say that?

Mercian, perhaps?

Oh, wouldn't that be nice? I can even get the decals for that.

I was able to weigh the frame and fork this morning. I used a decent, newish bathroom scale, and weighed them both by themselves, and with me holding them after taking my baseline weight. Results were consistent. Frame weighs 4.5 lbs, and fork weighs 1.5 lbs, for a total of 6 lbs even. That seems quite light to me, but my experience is limited. I seem to remember the old Cannondale aluminum frames were supposed to be 3.0 lbs; that was a big selling point back in the `90s.

I quickly considered and dismissed that option. I don't like irreversible conversions just for the sake of compatibility. It's a different case, if the shell threads have been stripped.

Again, I am a relative newbie at this. I have the tools and skills to build or fix bicycles - everything short of welding, but I don't have the extensive knowledge that many of you have. That said, I am wondering what sort of complications having a BB 2mm narrower than standard will present. On my French bike (with English threads - Taiwan mfg?), I used a square-taper cartridge BB where the cup-and-cone used to be; and that worked fine. If the threads on this frame are English, I plan to do the same. Am I overlooking anything?

Don't know for sure yet. I've seen a fork crown on Velobase that looks just like this, except the point is intact. If this is the same fork crown, then somebody filed the bottom off it for whatever reason.

Yes, that's on the light side, but consistent with butted 531. My frames are bit bigger, and the butted 531 ones weigh 72-78 oz form the frame, 23-30 oz for the fork. Nice.

With the comparison to the Steelman frame, the similarities are really superficial. Frame builders buy lugs and don't often change them very much, though they may refine the shape, tidy up the edges, thin them where that seems appropriate, etc. So while there's a similarity in the lug shape, it doesn't mean much, but the stay treatment is completely different from yours, and that means a lot more. The Steelman fork has a completely different crown shape.

I've been puzzling over this cryptic response. (Of course, I am old enough to remember the gameshow.)

Or is there a deeper meaning...?

I think T-Mar is in the right track, Cilo or some other Swiss.
To confirm, a French adjustable cup would be handy. Very few have a Swiss LH thread fixed cup on hand. If it is Swiss, locating a bottom bracket will be an adventure. As the shell is under width I would consider a Phil bottom bracket, width problems solved. To stay with a traditional assembly then careful measure will be needed to decide what side the spacing washers need to be used.

The narrower bottom bracket shouldn't be a problem. The only thing I'd be doing is measuring the distance relative to the seat or down tube, so determine how much was removed from each side. Any amount removed from the drive side can be compensated with a spacer behind the fixed cup. Amounts removed from the adjustable cup side do not require compensation. Some owners have been known to face the fixed cup side of the shell to compensate for chainline issues.

+2, Semper Fi

Another wing wipe type, You swing with the wing.....

Oh, nice frame, following with interest until you answer your question, and hopefully while you follow up with a build thread, too.

Bill

[MENTION=429363]DQRider[/MENTION] - no deeper meaning. It was the first think that came to mind when I read the title of the thread. I watched a lot of TV in the '70's.

Yes, there will definitely be a build thread. Having been a moto-journalist for a while, and a blogger after that, I go into withdrawals when I don't have an outlet for my writing and photography. It's a sickness, I tell ya!

Swiss is available without paying for Phil Wood, Italian, French and Swiss Bottom Bracket Conversion Cups ? Interloc Racing Design / IRD

Just not his style (IMHO): Steelman Cycles History
But, I've been wrong before! If he replies and says he made it I'll be amazed but will eat crow.

Also not buying the "Cilo" connection tho that's a little more plausible but AFAIK the "pointy" stay caps that early Cilos used are still different: the OP's
caps looks much more like some early Brit builders (and the occasional French "Contracteur") have used...but too many possibles to narrow it down.
Another detail: I believe Cilo would have used metric dimension tubing as well as Swiss or perhaps FR threading in the BB, plus they favored Nervex or BCM lugs.

I know his history. There's nothing on the page you posted that has anything to do with what his early frames looked like. Probably not a Steelman but it looks similar so I threw it out there, it's worth a shot, so what. A comment about an April fools joke was odd when even you have no clue what the OP's frame is. This is the vintage section, not the road section or the Paceline. No arrogance needed here.