The classification of elbows is based on their curvature radius, which can be divided into long-radius elbows and short-radius elbows. Long-radius elbows refer to those with a curvature radius equal to 1.5 times the pipe's outer diameter, denoted as R=1.5D. Short-radius elbows refer to those with a curvature radius equal to the pipe's outer diameter, denoted as R=D. In the formula, D represents the elbow diameter, and R represents the curvature radius. If classified by pressure class, there are approximately seventeen types, which are the same as American pipe standards, including: Sch5s, Sch10s, Sch10, Sch20, Sch30, Sch40s, STD, Sch40, Sch60, Sch80s, XS; Sch80, Sch100, Sch120, Sch140, Sch160, XXS, with STD and XS being the most commonly used. By angle, there are 45o elbows, 90o elbows, and 180o elbows. This results in a wide variety of elbow types. When placing orders, the specification method is often as follows: for example, "LR STD 90o 8" indicates a long-radius elbow with a STD pressure class and an 8" 90o bend; or "SR XS 45o 4" indicates a short-radius elbow with an XS pressure class and a 4" 45o bend. The above is a general overview of elbow classifications.