These are 8″ x 2″ x 1/2″ Bench Stones made by Tennessee Abrasive. They are made in Erwin, TN USA. They are made with high quality aluminum oxide and cut the material quickly.
THIS STONE DOES NOT FIT IN THE MASTER SHARPENER.
The ends are painted to indicate grit:
Green: 220 grit (coarse)
Blue: 600 grit (medium)
Yellow: 1,000 grit (fine)