Which headset do I need?

Bought this frame a while ago. The seller is sure this is 1 1/8. But which kind? I've only dealt with threaded headsets before and this jungle of threadless "standards" is driving me insane. The inside diameter is close to 38mm. Reading the charts at Park Tool and Cane Creek this would indicate IS38 aka 1 inch integrated. This would truly suck as the fork I have is 1 1/8. To me the only other option seems to be EC37 aka 1 1/4 conventional. This would be a lot better. But the machining of the inside and outside of the head tube seems weird for an external headset doesn't it? Damn I just want to get out and ride my new bike :/

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what is the frame ?

Mercian Pro Lugless. This one actually.

if your caliper is accurate then a measurement of appx 38mm points to an integrated 1" headset, have a read of this and see if you agree > https://www.canecreek.com/resources/products/headsets/technical-specifications/headset-identification-and-specification-guide.pdf < taking more meausrements, of both upper and lower tube will help establish an average diameter.

I actually re measured with a ruler earlier today (lol). But to my disappointment the caliper is correct. The lower tube has the same inside diameter as the upper. The "bearing depth" is hard to measure but its deeper than the upper (as it should be according to the pdf). Also it doesn't have the same outer machining. Haven't had the time to clean out the excess paint but here it is:

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1" integrated i'm afraid :(

give james NQ a duffing

I even had the fork (the one in the ad) painted to match the frame! Looks splendid! Oh well... I´ve messaged NQ. Lets see what happens.

This frame was 100% made for this fork as I stripped it down after riding the bike complete!

Great, so now we know that the fork fits the frame. The fork is 28,6 mm - 1 1/8". Measured it (once again) this morning. So the 1 inch integrated headset wont work. What will? The plot thickens.

You could ask James NQ if he has the original bearings for reference

Yeah I´m hoping @JamesNQ will be able to point me in the right direction...

Headset was completely internal, don't have any information other than that I'm afraid!

James

did you bin it?; if it's still lying around then a good probability it will have type information lasered onto the outer ring

I've contacted Mercian now. Looking at their website this is probably the "Wiglaf" model, not the Pro Lugless. If that is correct, the headset should be 1 1/8 integrated. I didn't even know they had that model until now.

good sleuthing scott, still curious as to how a 38mm recess can accommodate a 1 1/8" headset, must be some awesome inverse shimming!

Yeah the inverse shimming thing is seriously weird. Gonna wait til I hear back from Mercian before I put in the order.