These Milwaukee Road-designed caboose/passenger trucks came in two different variants - straight frame or drop frame. The original straight frame trucks were first used on some 56' combines built in 1934. Cabooses 01800 to 02014 were equipped with the straight frame design, while 02015 to 02114 had the drop frame design (beginning with the 1949 cars). The drop frame trucks provided a better ride, and in later years were used on cabooses in mainline service (whereas the straight frame equipped cabooses were used on branches and locals).
At present, the only N scale trucks in this style are made by Fox Valley Models (for their Milwaukee Road rib-sided cabooses) -