There were 4 quite different K4s locomotives made by Samhongsa in 2 and 3 rail O scale versions. Around 1986 a pair of K4's were simultaneously imported by Williams. I briefly was a local dealer for Jerry Williams and sold quite a few to DC area O scale 2 railers. One version of the K4s was the classic non-modernized pre-war front end, while the other was a model of circa 1940 streamlined K4s number 1120 (one of 4 similarly streamlined K4s) . Note that this streamlining was totally different from the circa 1935 Raymond Lowey styled K4s 3768 (a.k.a. the "Torpedo"). In addition to K4s models, Williams imported Samhongsa models of PRR's L1s, B6sb, and and E6s. At some point in the 1990's Weaver supplanted Williams in importing Samhongsa built brass O scale 2 and 3 rail locomotives. The first Weaver/Samhongsa brass steam locomotive was a PRR M1b, followed by quite a few other PRR prototypes including streamlined K4s 3768,(the Torpedo), a modernized K4s (1361??), A5s, H10s, G5, and T1. As others have pointed out Samhongsa built Williams and Weaver brass models were solidly built and smooth running - albeit with relatively austere details by today's standards. Some dimensional compromises were made in (boiler/smoke box/pilot length) to enable the same chassis and boiler to be used for 2 and 3 rail versions. The Williams B6sb and Weaver A5 however are spot on scale length and are excellent starting points for super detailing by rivet counting SPF's.