Sold individually, not a set.  Buy 3 get 1 free!  Also called finger towels, they are used to dry the fingers after cleaning both during the before communion preparation and during the post communion ablution.  They may be used over the arm of an altar server to aid the celebrant, so they are publicly visible.  As with other linens, it is best to keep a few around, (ie: tucked under the votive table, beside the lavabo bowl, or in the burse).