This is for ONE piece.  

With M10 x1.25 threads both internally and externally

Choose R/H-R/H for most models

Choose R/H-L/H or L/H-L/H for most Yamaha etc. 

The 1st pair of letters refer to the female side that the mirror screws in to

The 2nd pair of letters i.e. L/H refers to the direction of the thread on the male side that screws into where the mirror used to screw in to