This is a Tri-Grit Sanding Stick from Squadron Products.
Three grits for shaping, buffing and polishing
Resembles a fingernail file
Can be used wet or dry
Can be cut and shaped to fit specific areas as needed to achieve the
finest finish possible.
One Tri-Grit Sanding Stick
Length: 5¾" (146mm)
Width: ½" (12.7mm)