The Philistine blacksmiths charged 1/3 ounce of silver for sharpening plows and hoes and 1/6 ounce of silver for sharpening picks, axes, and the iron tip on ox goads.
Only the Philistines could sharpen iron tools. So if the Israelites needed to sharpen their plows, hoes, axes, or sickles, they had to go to the Philistines.