Found these awhile back on a pre 1860's house site, but just came across them again. Brass, about 2" long. PATD 1869 or 1860. Threaded hole on one end and the other side opens when the bolt is put in.
Nokta FoRs Gold, a Gold Cube, 2 Keene Sluices and Lord only knows how many pans....not to mention a load of other gear my wife still doesn't know about!