The whole derrick is set up by keys, no mortices or tenons being used, and thus the complete rig may be readily taken down and set up on a new site.
On their level tops the beams supporting the platforms were laid and fastened by wooden pins, or inserted in mortices cut in the heads of the piles.
Those pieces are connected at theii joints or surfaces of mutual contact, either by simple pressure and friction (as in masonry with moist mortar or without mortar), by pressure and adhesion (as in masonry with cement or with hardened mortar, and timber with glue), or by the resistance of fastenings of different kinds, whether made by means of the form of the joint (as dovetails, notches, mortices and tenons) or by separate fastening pieces (as trenails, pins, spikes, nails, holdfasts, screws, bolts, rivets, hoops, straps and sockets.
The case is almost complete, and empty mortices and slots show the precise positions of a few missing back and side panels.
The crests have wood spigots which are mounted in slots or mortices in the cornice frame.