This month's mystery item is a scythe sharpening and honing stone. Scythesupply.com does a great job explaining how to use this handy little tool:
"Use the narrow, curved face of the stone. For a grass or ditch blade,
rest the stone’s curved face simultaneously on the blade’s rib and edge.
Stroke the stone towards the edge, keeping its face in contact with both
rib and blade edge. This will produce the correct bevel required for a
grass or ditch blade."
"Continue in this manner from heel to the toe of
the blade, overlapping the strokes. To remove the wire edge from the
underside of the blade, turn the blade over with the edge facing away
from you. Lay the narrow edge of the stone against the blade edge and
pull the stone backward, away from the edge. Do this lightly, overlapping
the strokes from heel to toe.
A bush blade is sharpened the same way except the heel of the
stone is raised above the rib slightly as the stone is run along the
edge. This gives the edge a higher angle and more metal behind the edge
for strength."
This month's mystery item is a scythe sharpening and honing stone. 
"Continue in this manner from heel to the toe of
the blade, overlapping the strokes. To remove the wire edge from the
underside of the blade, turn the blade over with the edge facing away
from you. Lay the narrow edge of the stone against the blade edge and
pull the stone backward, away from the edge. Do this lightly, overlapping
the strokes from heel to toe.