Bypass pruners usually work exactly like a pair of scissors, with two blades "passing by" each other to make the cut. At least one of the blades will be curved: a convex upper blade with either a concave or straight lower one. Some bypass designs have only one blade, the lower jaw being broad (like an anvil) but passing the upper jaw. The ratchet pruner, which can handle stems thicker than two centimetres, fits in this category. Because they make a clean cut without crushing, bypass pruners are preferable for pruning live wood.