They are the same model ( 20 stands for 20” & 510 stands for 510mm). It is the same for the FT610 & FT24
Shaver Blades on an FT or Supersix model with a 10w bladed cylinder are ‘Shaver Std’ (90 thou)or‘Shaver Thin’ (60 thou)- FT or Supersix models with 5 Bladed Cylinders are ‘Lipped blades’
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