Bettendorf

In 1903 Bettendorf introduced a truck with a T section.

Introduced in 1903, the Bettendorf friction bearing truck was one of the first truck designs with one-piece cast sideframes and integral journal boxes. The original design used a sideframe with a "T" cross section. T-section trucks remained popular through the twenties, but were eventually phased out in favor of newer designs (and ultimately banned from interchange service in 1953). The Bettendorf T-section truck has never been modeled in N scale, so here's Kadee's HO version (hey, we can dream, can't we?) -
Significantly stronger trucks featuring a U-shaped cross section eventually superceded the T-section trucks starting in the 1920s. This style of truck, which is most identified with the modern steam and early diesel eras, has become generically (and incorrectly) known as the "Bettendorf" truck. The Bettendorf Co. widely licensed elements of its design, so many builders besides Bettendorf made trucks of this type (to the point that the U-section cast steel truck was eventually adopted as an ARA standard: the Type Y truck). Although each of these trucks (regardless of the manufacturer) follows the ARA/AAR standards, many have varying details (sideframe shape, spring size and styles, bolster design, journal-box lids, etc).
Starting in the 1930s, these trucks were upgraded with double-truss sideframes (with parts of the U-shaped section being filled in, creating a double-layer effect on the sideframes). Model-wise, these trucks are indistinguishable from the earlier U-Section / Type Y trucks.
Virtually every N scale manufacturer has offered up some sort of "Bettendorf" style truck at one time or another (and of varying quality). These are generally presumed to be 50-ton trucks, although Atlas does make a 40-ton version (for use on lighter cars such as reefers).
Athearn, Atlas/China, Atlas/Roco, Bachmann (new), Con-Cor, Fox Valley, Intermountain, and Micro-Trains 50-ton -