From their announcement:
When laying siege to an enemy, a Chaos Dwarf Daemonsmith will sometimes remove the fell cannonades of an Iron Daemon and replace them with a hissing and grinding arcane-mechanical conglomeration of iron hammers, hacking blades and brutal picks. Designed to smash down walls and tear fortifications asunder, the cruel blades of the so-called Chaos Dwarf Skullcracker are equally adept at pulverising the flesh and bones of any enemy unfortunate to be caught in its implacable path.
The Chaos Dwarf Skullcracker is a highly detailed full resin kit, designed by Tim Adcock, and is supplied with three unique crew figures designed by Thais Mariblanca Lopez. It is available to order now, and full rules for this nefarious device can be found as part of the Legion of Azgorh army list in Tamurkhan: The Throne of Chaos.