I'm definitely no mechanic, so I'm sure someone will come along later to explain and correct me...... As far as I understand it, the clutch wears out on one side (the one nearest the plates) and to prolong its life (and to save you money) that part of the clutch can be turned round so it evely wears down. Now, told you I wasn't mechanical, I can't even remember the damn name of the part!!
Ade.