Used only on the larger 9" cars until the newer T trucks were introduced in 1910, these trucks are unique in that they are entirely inside the wheels. 

Commonly called T Trucks these can be found on both 9" and 6" cars. The 9" cars shown above only used T Trucks until 1912. The 6" cars used T Trucks until 1917. In the above picture the truck on the right has been lacquered the one on the left has been painted.

First used in 1912 on the One Gauge passenger cars, these trucks are only found on the 9" cars.

Type A (1917) - Not sure what was going on here, but the first 'M Style' trucks were NOT embossed, simply plain flat sided. These trucks appear to have been used only in 1917 and for the most part only on 6" passenger and freight cars (*Exception)

Type B (1917-1924) - Same truck as Type A above except now it's embossed. 

Type C (1925-1928) - In 1925 Ives started putting journal boxes on the 9" passenger cars, so slots were punched in all the trucks. 

Type D (1925-30) - M trucks with journals Used on 9" cars in 1925, brass plate pass. cars in 1926, used on all 8 wheel cars starting in 1928. 

Type E (1929-1930) Flater truck than type D and has extra slots in center for a third set of journals that were never used. These trucks were originally made for a planned 1929 set called the Cascade Limited. The 141-142 cars from this set were supposed to have six wheel trucks (actually 4 wheels with 6 journals). These trucks show up on the larger brass plate passenger cars from 1929 and 1930 and obviously from the picture above, some No. 25 tenders. 

Late trucks with pickups for lights - note the insulated axle and the fiber board that it connects to.