Carol, you don’t actually have to make the blade thickness a multiple of your nozzle - your nozzle can extrude different widths. However, you do want to make the blade thickness a multiple of your extrusion width. If you change the blade thickness and don’t also change the extrusion width in the slicer it can lead to gaps.
My rule of thumb is to set extrusion width to 1/2 of the blade thickness + 0.04. So for example: if you want to print a 0.9 mm blade. By default the slicer will have a wall thickness of around 0.4, so two walls will be 0.8 and that will leave a 0.1mm gap between the walls, which may be too thin to fill. The solution is to set the extrusion width (in cura it’s called line width) to 0.49. A 0.4 nozzle can print a 0.49 wall - and that solves the gap problem.