Normal width is 8/9/10/12mm.
 

which is sewn on the bra to take a bra wire. Specially made to be strong enough to prevent the bra wire poking through. This is a lighter version than our other bra casing, being made of tricot. Many bra patterns s est how to make your own casing, and this is a factory produced version of a similar weight. It is easier for the home sewer to use as it doesn't catch so readily under the foot as the heavier grade, which would be attached by a special machine in the factory.