The March 15, 1940 Master Parts Catalog begins with part number 9N-400-A -Seat Assy. (Steel); followed by 9N-400-B -Seat Assy. (Plastic). Both are fastened to the spring (9N-404) with a 7/16-20 Carriage Bolt; lockwasher; and hex nut. I have seen only one original plastic seat in my life. Most were eaten by field mice. Henry Ford was experimenting with polymers from soybeans and tried to make several parts with it, the tractor seat being one of them. The seat idea was a failure and was soon dropped from production. By 1942 only the steel seat was offered. The January, 1946 MPC shows two seats, 9N-400-A (welded) and 9N-400-C (riveted), both assumed to be steel. Unsure what 'welded' and 'riveted' define. The early 9N seat has 9 breather holes on the back of pan. There may be exceptions to this, however. The 9N-400 seat was not of the flip up design. The hinged style seat was not introduced until the 8N in July, 1947 and was one of over 40 new features offered on the 'new' 8N Model. The 8N-400-A pan seat only has 4 breather holes. The May, 1949 MPC shows two different seat springs, one longer than the other.
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