Honda Civic manifold stud. Any parts store on the planet should have em in stock, no?
Is something like this really more than a few USD equiv where you are? Otherwise, +++ on the 6mm black oxide Allen head bolt. 10.9 grade or so. Get a few longish ones, 50mm 'bout. Don't need a die to chase the cut thread. Thread a nut on the good side and when it comes off the cut side it'll align the thread good enough. Wire wheel the rest if needed. (edited)