Learn how pp and ss measurements equate to millimeters, a more commonly used measurement in jewelry making and beyond for PRESTIGE crystal flatback rhinestones. Pearl Plate (pp) Stone Size (ss) Millimeter (mm) 11pp 5ss 1.8 mm 13pp 6ss 2.0 mm 15pp 7ss 2.2 mm 17pp 8ss 2.3 mm 19pp 9ss 2.6 mm 21pp 10ss 2.8 mm 24pp 12ss 3.0