SPC Section V Belts 22 x 18mm.

SPC Section Belts are measured on the PITCH (Lp) length in mm - The Pitch (Lp) measurement is taken from in between the inside (Li) and the outside (La)

Use the following to convert your measurements:

Outside (La) to Pitch (Lp) - 30mm 

Inside (Li) to Pitch (Lp) + 83mm