We needed to replace an old 1/2”-12 bolt that was missing from our Challenge guillotine cutter. (12 threads per inch is not standard, 13 is, so new 1/2”-13 bolts don’t fit.) Turns out that an old British size is a suitable replacement. British Standard Whitworth (BSW) 1/2-12 totally fits. Ordered ours from British Tool Fasteners in Lyons, NY.