Diamond coated round section steel hones with plastic handles for sharpening blades such as ring tools and hook tools. Also performs well instead of a slipstone to take the burr off the inside of gouges. Tapering from 3mm to 9mm, the blade is 100mm long. Fine grit.
Works on tungsten carbide as well. Can be used wet or dry. Very useful in the kitchen as a knife sharpening steel but keep that a secret!