What is the fourth hole on a road shoe sole for?

jehannum5
jehannum5 Posts: 54
edited March 2012 in Road buying advice
I was fitting cleats to my new sidi mtb shoes and I was browsing the instructions. I,noticed that their road shoe range has the standard look drilling and a fourth hole in between the lower two holes. I was looking further and noticed that all the cleats that were illustrated occupied only the look holes and none used the fourth.
Now I remember in the nineties an intermediate spd-r cleat that was metal and used longitudinal cleat holes (from memory). Is it possible that sidi still accommodates these cleats? I thought they may have been for speedplay however the guide recommends attaching the cleat to the three look fittings.
Anyway just curious.

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