Sh51 spd single release cleats recommended for all mtb spd pedals except pd m858 release the cleat by twisting heel outwards in laymans terms this is the cleat that will fit 99 of spd compatible pedals excluding the pdm858 sh52 spd single release cleats recommended for pdm858 pedal release the cleat by twisting heel outwards in laymans terms this is the cleat that will fit all of the same pedals as above sh51 and also the pdm858 unless you have the pdm858 wiggle would recommend o