It's from a steel frame which clamps a 27.0mm post and there isn't much / any thread protruding so you may be correct. With the bolt flush with the end of the nut the verniers measure 27.25mm of internal bolt (funnily enough) so it is probably too small. No dramas.
I've a couple of nice tyres on eBay currently, ending Sunday evening. They haven't attracted (m)any followers unfortunately so here are the links in case you're interested.
Ritchey Mega Bite Z Max 2.1 Severe Condition 26" Folding Tyre, Black:
https://www.ebay.co.uk/itm/Ritchey-Mega ...
Finally got around to tidying the garage and found a few bits which might be of interest. This is my first foray into selling on here so please put me right if there are any issues. Payment via PayPal F&F please. Photos in the following two posts.
Kool Stop Eagle Brake Blocks, Green, x4 - £10...