Hi rfvdveldt

The 28-50 tractor you have was built in 1930. 71701 was the last 28-50 produced so your tractor 71691 is a late one.The first 28-50 with the wide radiator was made in 1928 serial number 70952. 450 narrow radiator tractors were made before the wide radiator tractors.
    The 12-24 serial number 40534 was made in 1929 and is a 12-24 H. The H tractor has a 3 speed transmission and a 5 3/4 bore engine.
   The 18-36 serial number 34960 was made in 1929. It is a 18-36 I. The I tractors were the last 18-36 tractors produced. These tractors have a three speed transmission.
   All the tractors were built in Charles City Iowa.To the best of my knowledge no records exhist showing where they went when they left the factory. Production of all Hart Parr light weight tractors ended in 1930.-----Hoov