An Eperon is a strange shape, unique in that it is a combination of two shapes, but typical to French stoneworking professionals. They are extremely efficient in shaping your work.
Knife shape with a cut edge and the inusually termed "Crete de coq" which has a spur as shown in the photograph.
The Eperon is stitched on both sides. The longer the tool the more aggessive the cut.
These are precision shaping tools so look carefully at the range and decide what best suits your needs.