Fine Round Rubber Leggs are a critical now days on many patterns. They add lots of lifelike wiggle.
They work well tied in X style on dry fly patterns like adult stones and tied on the side on your nymph thorax's.
Either one will give many of your flies a distinct advantage.
Caution...do not store them in direct light. Like a rubber band...they will eventually rot.
Sold as a strip about 1" wide and 18" long.
Fine size is about 1/2 mm in diameter.