"Warning - the newish Shimano cleats with rubber pontoons (SH71) will not work with Shimano A520 SPD pedals. The rubber outriders foul the pedal and you cannot lock-in.
I was foolish enough to file them down thinking they would work when they were more worn down, Wrong! I managed to get the pedal/cleat locked together but then could not release them. Eventually I had to dis-assemble the pedals to free them."