Bone Casing: 1/2-inch Wide Black Per 20YD Roll 10% DiscountPriced per 20 yard roll. Black. Bone Casing. Bones are slipped into the opening between the two layers of the casing. For use with 1 4 inch bones. Perfect for ballet costumes and any costume that is sweated in gives another layer of fabric between the body and outer bodice fabric, so minimizes rust stains caused by steel boning becoming wet with sweat. Need less? See Discounted 5% per 5 yard roll, and yardage product pages.