In the early 1900s, center-shafted, mallet-headed putters, such as the Schenectady model, were becoming increasingly popular in the United States. In 1910, The R&A added two new Decisions on the Rules of Golf that spoke to croquet mallets specifically and deemed “the various mallet-headed implements” to no longer be permissible for use. However, the USGA interpreted “mallet-headed” differently and continued to allow putters like the Schenectady and Hackbarth models to be used in the United States.
This difference in interpretation between The R&A and the USGA was rectified in 1952, when both organizations came together to jointly release the first uniform code of the Rules of Golf to be used worldwide. At this time, it was decided that the putter shaft could be fixed to the putter head at any point, which permitted the Schenectady putter, and other similar styles, to be used anywhere in the world.
The Hackbarth model mentioned above, however, is no longer permitted because of the way the shaft connects to the clubhead.