Nice 5" Mouth training bit.  Commonly used with 2 reins, one connected to the bottom ring for the curb action, one connected to the D for direct reining.  As training progresses the D rein is removed.  The D itself is helpful though as the horse can feel the slight pressure on the side of his mouth from the D when the curb rein is used.  This property makes this a very popular bit for training horses to a full western bridle.

Stainless steel by Madco