Though testing was complete on fully equipped trains in 1930, this style didn’t become standard until 1956. Then in 1966 the A.A.R. made them required on all new cars. Rebuilt cars were included in 1970 and by 1978 more than 70% of North America’s rolling stock was roller bearing equipped. Micro-Trains N 00302032 (1033) Roller Bearing Trucks with Medium Extension Couplers (1 pair, Assembled) With Medium Extension Couplers