Feb 27,1883 was original Acme patent 273170 . Evidently several companies used that patent and Whitman & Barnes was one of them. Datamp says some were made with twisted handles like the Acme and some with straight handles. Still don't know why some were made with thread on back rod and some with thread on rod on jaw side although intuitively it would seem like jaw side thread would give better grip with less flexure.