Seat off the tractor was listed as a hydraulic seat attachment on a M from may 1948 and up to the start of stage 2 SM tractors. Like other attachments it was more common to get tractors with the attachments installed on the newer models. Seat pictured this time was a hydraulic seat attachment for a M in 1947 and 48. Don't know if IH purchased both types from Monroe or what, but they listed them under IH numbers for the seats and parts. this picture of new ones from a 1947 train wreck shows the Monroe type installed when shipped.