Source : Webster's Revised Unabridged Dictionary (1913)

Hemmer \Hem"mer\, n.
   One who, or that which, hems with a needle. Specifically:
   (a) An attachment to a sewing machine, for turning under the
       edge of a piece of fabric, preparatory to stitching it
       down.
   (b) A tool for turning over the edge of sheet metal to make a
       hem.