They were optional on some models such as my 38. mine is the long wheel base without helper springs but I have seen short and long wheel base with them. less equipment standard meant lower cost buyer could add what they wanted. My grandfather said he intially tried to get by with adding leaves to the helper springs to increase the capacity on his 47.2 chevrolet tractor but when he loaded it the helper springs caught the brackets and broke them off. better to build up main spring. Can't imagine how rough that would ride empty.