Skewed hollows and rounds
British plane makers regularly made hollows and rounds with skewed irons. Some American manufactures did also (for instance Ohio Tool Company made sets numbered 72 1/2 and 73 1/2) but they are fairly rare. Most American joiners and cabinet makers did not use the skewed irons. My set of user hollows and rounds was made by the English plane maker Varvill and Sons. and are skewed.
One quick way to tell English planes is the bedding angle of the iron is usually steeper, most being a York pitch or about 50 degrees.