SHORT VS LONG RADIUS ELBOW
The center to face distance of a long radius pipe elbow is always 1.5 times the nominal pipe size, whereas, for a short radius pipe elbow, the center to face distance is equal to the nominal pipe size.
For a 4 inches long radius (LR) butt weld elbow, the center to face distance is 4 x 25.4 x 1.5 = 152.4 mm;
For a short radius butt weld elbow, the center to face distance is instead 4 x 25.4 x 1 = 101.6 mm. Short radius pipe elbows are available only for the 90 and 180-degree configuration (and not for the 45 degrees); instead, long radius elbows are available for all degrees.