The patent is for a groove in the inside face of one half of the tool, and a ball stop on the inside face of the other half, positioned so that the stop aligns the wire cutter notches fully open and ready for use. The pliers jaws are incidental and not part of the patent claims. Vaughan & Bushnell added "Button's pattern pliers" to their product line starting in 1901.
Compare the internal stop in patent no. 1,018,839 (Buffum Tool Co.).