This set of trucks is a pair of equalized Union Pacific Roller Bearing Outside Swing Hangar Trucks for UP cabeese. These trucks are designed for 0.540 lo profile flange axles and attached with a Micro-Trains bolster pin.
These Outside Swing Hangar Trucks are perfect for IRC/Centralia Car Shops latest run of Union Pacific CA-3 & 4 Cabooses, which have incorrect generic caboose trucks. These trucks will fix that problem. Friction bearing versions went on Armour Yellow CA-3's & 4's starting in 1952. 1969 thru 1977 saw adding the roller bearing version to Pool Service Cabooses with two CA-3's and seven CA-4's being converted in 1975.
For Cabeese with Friction Bearing Q trucks, see: https://www.shapeways.com/product/XEZ4G2FRA/n-scale-up-friction-bearing-q-truck-2pk
CA-8 and above had INTERNAL generators. For Cabeese with Roller Bearing Q Trucks with an external generator, see: https://www.shapeways.com/product/FJTX34XGK/n-scale-up-roller-bearing-q-truck-2pk-w-generator