The hollow, roughly 25 by 22 centimetres across and about five centimetres deep, is the defining feature that makes this an unremarkable-looking stone something else entirely.

Bullaun stones are boulders, usually granite, into which one or more cup-shaped basins have been ground or pecked, almost certainly by human hands. They appear across Ireland in considerable numbers, often near early medieval ecclesiastical sites, though their precise purpose remains genuinely uncertain. Some were likely used for grinding, others are associated with folk cures and votive practice, with rainwater collecting in the basins considered to have curative properties. The Drummin example measures 1.1 metres by 0.7 metres and stands around 0.6 metres high, a solid, low-slung stone that would be easy to walk past without a second glance. Its current position on the field margin is almost certainly not original; it was most likely shunted aside during agricultural clearance of the adjacent ground, which is a common fate for these stones and one that severs whatever spatial relationship they once had with a nearby site or feature.