This cast iron shot had a wrought iron spike (pointed at both ends) going through the centre, leaving a square hole.
A good description is “spike shot”, but this term seems interchangeable with “crossbar shot” within contemporary or near contemporary descriptions/inventories. The spike did not survive in the silts, so we have replaced them with frosted acrylic.
Primarily for tearing sails, sometimes the ends of the spikes were wrapped with incendiary material so they would burn sails, and indeed some of these did show up in radiographs of concretions recovered from the wreck site.