Rockwell B and Rockwell E are both used for measuring the hardness of aluminum alloys, but Rockwell B is noted for its wider applicability. Rockwell B employs a 1/16" steel sphere at 100 kg, while Rockwell E uses a larger 1/8" sphere, which may affect the accuracy of measurements. A key consideration is that the specimen thickness should be ten times the indentation depth, making Rockwell E suitable for thinner samples. However, Rockwell testing is limited in its ability to provide convertible hardness values, with Vickers being recommended for more accurate conversions. Ultimately, Rockwell B is favored for its broader range, despite the specific needs for aluminum alloys.