Hi,

I am still confused about ISO metric thread and tap standards.

So does same designation thread and tap fit together? For example, M5x1.25 thread can be used a M5x1.25 tap?

Thanks for any info!

Yes - the M10 x 1 designation specifies a bolt of nominal diameter 10 mm and thread pitch of 1 mm. If it's specified as ISO metric then that defines the height and angles of both the internal and external mating threads. So a thread cut with an M10x1 ISO metric tap is intended to accept an M10x1 ISO metric bolt.