Crower had ductile iron rockers available in the late 1970s that looked like that. They had no lock nut and had an interference fit on the adjuster. When I bought them new and got them I was unsatisfied with the adjuster arrangement being concerned that they would not hold adjustment. So I called Dave Crower and expressed my concern. I recall that switching them over to a standard adjuster with a lock nut was really not an option as the threads were unique. Dave agreed to take the rockers back. I then bought the Iskys (which were more money). Still have the Isky's today.