These are toppers to add detail to 25mm bases for gothic-themed 28mm miniatures and others. They're not full bases in and of themselves, they're not quite 25mm wide and a little short for that. Instead they go on top of a standard plastic base. The intent is to match the now-discontinued Imperialis Basing Kit that Games Workshop made a few years back that worked the same way, so new troopers can match figures made with it.
Ten styles are included in this set, each with a complete version and three cut-up variants, again to match the partial pieces of the Imperialis Basing Kit.