I also think it is a tap wrench, According to trade pattern books rectangular ends on taps seemed to be generally common prior to about the 1850s, and they were two taps per set ( a tapered thread tap and a parallel tap) Though top British engineers like Maudslay, Clements and Whitworth were using (modern!) three set square drive (drop through) small shank taps as early as 1828 (English and American tool Builders By J W Roe)
Graeme