where it attaches it's the size of a worker cell, about 4.9mm to 5.0mm or so. Roughly a quarter of an inch. The mouth of the cell (at it's widest) is about 5/16" (inside). The length I've seen vary GREATLY from 3/4" to several inches. But typically they are about the size and shape of a peanut except a little smaller on the small end.