Quite a lovely and smart looking thing, this hand-engraved silver square and compass tool would have been made for a Masonic "Senior Deacon."  Through a little research I've learned it would have been carried by the Senior Deacon when guiding candidates through the rituals associated with attaining their masonic degrees. (Specifically, I've read, the compass would--symbolically I presume!--be used to "pierce their naked left breast," or the square "applied to the same.") Together the compass and square symbolize ethical conduct, and self-discipline within Freemasonry, with the square representing morality and acting with integrity, and the compass signifying boundaries and the relationship between individuals and society. 

3 3/8" long x 1 1/4" overall. Straight edges just shy of 3" (long lines on ruled edges mark the half inch--then divided into eighths of an inch). I've found one other example out there very similar to this one down to the details of the engraving (that one housed in a Masonic museum, and monogrammed and engraved with a lodge number.) Later 19th century would be my guess, this one found in central Massachusetts.  While there is no mark, it appears to me to be silver. (Not magnet attracting, tarnish wipes off black; I lightly polished one edge to test it (some photos taken prior to that) and it shines up beautifully. Nice condition, opens smoothly to a square and closes tight and flush.