Blueprint was revised in 1976.

The vintage railroad blueprint is for a Soo Line Ballast Car, specifically the HK model, which was built by Rodger Ballast Co in 1937 in the United States. This blueprint provides detailed specifications and schematics for the construction of this particular type of railcar, which was likely used for transporting ballast materials for railway maintenance and construction. The blueprint offers a unique glimpse into the design and engineering of railroad equipment from that time period.