Constructed of stainless steel with dual diamond grit surfaces. 4-Inch model has a fine (#600 grit) side, and medium (#300 grit) side. 6-Inch model has medium (#300 grit) and heavy (#150 grit) sides. Grooves on each side will sharpen hook bottoms and points and flat areas will hone sides of points. A bright yellow lanyard is handy for hanging it on your vest or finding it in grass or the water.