A boning knife is used to remove bones from cuts of meat. It has a thin, flexible blade, usually about 12 cm to 15 cm (5 or 6 inches) long, that allows it to get in to small spaces. A stiff boning knife is good for beef and pork, and a flexible one is preferred for poultry and fish.Filleting knives are like very flexible boning knives that are used to fillet and prepare fish. They have blades about 15 cm to 28 cm (6 to 11 inches) long, allowing them to move easily along the backbone and under the skin of fish. Shop a wide array of Boning & Filleting Knives at Bulmers Gifts.