What does 'ss' mean??

It means  'stone size'

All sizing from any manufacturer of stones is the same

ss4       1.5 - 1.6 mm

ss6       1.9 - 2.0 mm

ss10     2.7 - 2.8 mm

ss12     3.0 - 3.2 mm

ss16     3.8 - 4.0 mm

ss20     4.6 - 4.8 mm

ss30     6.3 - 6.5 mm

ss34     7.1 - 7.3 mm

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