The Blomberg B is a 2-axle bogie that was introduced by EMD in 1939 with the FT locomotive series; the original "B" version plus later "M" and "X" versions were quite successful and became standard equipment on a multitude of locomotive models. They are easily identified by prominent "swing hangers" on each side which widen the effective spring base and provide a better ride. EMD literature refers to this truck as the "2 Axle Outside Swing Hanger;" informally it is named after EMD designer Martin Blomberg; this design evolved as an abbreviation of the preceding 3-axle design from the E-units; see U.S. Patent 2,189,125 filed on Jan 29, 1938 and granted on Feb 6, 1940. As of 2022 Blomberg B trucks are common sights under operating locomotives throughout North America.
The "B" version is the original 1939 design. EMD Blomberg B trucks are seen on other makers' locomotives; this occasionally resulted when buyers of new GE locomotives preferred trade-in EMD trucks and/or motors, instead of GE standard equipment.
The M version (meaning "modified") was introduced in 1972 with the EMD Dash 2 locomotive series; it is also used on later models such as the GP50, GP60, F40PH and F59PH, as well as the MPI MPXpress.
The X version (from "express") was introduced in 2007 with the MPI MPXpress locomotive series; its formal model is MPI 2237. This version directly evolved from the Blomberg M, but is longer and thus not rebuilt from older Blomberg frames.