The blade of a fillet knife can measure 15–20 cm in length. More importantly, the width of the blade should be 1.5–2 cm, although certain knives have a wider blade.

To sharpen, the use of a honing steel is recommended.

Once a sole has been trimmed and cleaned (gutted), cut along the backbone starting at the gills. To cut out four sole fillets, gently slide the blade between the flesh and the bones on each side of the fish while tilting the knife. Above all, be careful not to cut through the flesh.