If you have ever made a salt or pepper mill or are thinking of making one, than these two chucks are indeed a necessity. Each chuck is specially milled to the exact size of the holes at the top and bottom of the drilled mill blank. Without these chucks it is virtually impossible to turn between centers. The large chuck which measures approximately 1-5/8" in diameter fits snuggly into the larger hole and fits neatly onto your lathe spur drive. The small jamb chuck which measures approximately 1-1/6" id diameter fits directly into the smaller hole and has a pre drilled hole on the other end for your center on your lathe. Each chuck is made from durable phenolic for years of use. Includes one each of the 1-5/8" and 1-1/16" jamb chucks.