Think you'll need M10 x 1.5 thread pitch like my 1996 XLM.
I tried Merlin first but they sent the wrong size, ended up getting some 6/4 Ti ones off e-bay. They weren't perfect as needed the shoulder machining down by 2mm so the pin on the rear of the brake would locate in the hole.
How old is your frame?
Compare your old stud with the 1.5 thread pitch stud - is yours coarser or finer thread?
If it's late '80s / early 90s then probably the imperial size Merlin used so contact them, or if it's very late 90s then most likely industry standard 1.25 thread pitch which your LBS should stock.
When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I took the remaining stud to an engineering supplier and he couldn't match the thread - but thought the closest match was UNC/UNF.
He pointed me to a small precision engineer who spent a considerable amount of time measuring and trying to match threads - his conclusion also was that it was UNF but that it seemed to fit between 16 and 18 pitch. He said there was no 17! I was goingto ask him to turn me a couple, which he will do - but obviously we needto be sure of the thread!
Merlin USA say they only have M10 x 1.25 or M 10 x 1.5 - but it's not either of those. I'm waiting on a further response from them, since there must be somebody there with access to records?