I've just replaced these stock bolts for Stainless Button head Cap screws.
The rear ones are 8 X 1.25 thread, which is a stock metric size, but the front ones are 10 X 1.25 which is fine metric and very difficult to find (as a button head)
The standard 10mm bolt has a 1.5mm pitch thread and are readily available.
Why triumph used a fine thread, I don't know.