May be incorrect but I have found after a year of searching that metric and BSP are the same. I have purchased Metric 10, 6 and 3 mm fittings and they fit what I though was BSP 3 /8, 1/4 and 1/8 BSP. Some of the fittings had both names. I would guess that piping may be the same. My local hardware had basic fitting.
I dont quite understand this as I dont know what the size relates to - may be the pipe size.