Spiral bones 3/16 inch (4mm) wide
4mm wide spiral bones - use two side by side in a casing.
German made spiral bones that are only 4mm wide (approximately 3/16 inch) seem tiny and ineffectual, but put two side by side and you get a design feature that's just as supportive as a 1/4 inch wide spiral. In the image here I've sewn down the middle of some 1/2 inch wide bone casing tape and slid two 4mm wide spiral bones into the newly created double bone casing. Another option is to use bias strips of coutil to create bone casings that curve - this method can be used with any size of spiral bone. Or use Prussian tape to create a single casing.
There is a 15% discount factored into the price of 50 meters
1 meter is approximately 3 inches longer than 1 yard
The grid is made up of 1/4 inch squares
A Canadian source for spiral boning.