The 400 Grit BW8 (photo shown is 150 Grit) is a wheel shaped diamond bur. The approximate head length is 4.5mm, and the approximate head diameter is 13mm. This bur is great for grinding or carving all types of stone, glass, tile, metal, wood and more... The 400 Grit is intended for smoothing and blending. It will not remove much material, and will leave you with a smooth, matte, pre-polished finish. The 400 Grit will still cut opal and works well for making small opal carvings or free forms. As with all Lasco Diamond Burs, the 400 Grit BW8 is a high quality, durable, 100% Natural Diamond bur, and is made in the USA. The BW8 is also available in 80 Grit, 150 Grit, 200 Grit, 400 Grit, and 600 Grit.