The block is modest in scale, roughly 32 centimetres by 30 centimetres, flat-topped, and carved with a circular socket set within a larger incised circle, with two opposing radial lines running outward from the socket to the circle's edge. It looks deliberate, considered, the product of careful hands, yet its original purpose has remained a matter of quiet academic dispute.

The object was recorded by R.A.S. Macalister in 1916 and 1917, at which point it was located in the Saint's Graveyard on the island. It has since been moved to its current position just north of the church doorway. Macalister classified it as a possible cross-base, the kind of socketed stone block designed to hold the upright shaft of a free-standing stone cross, which were common features of early Irish monastic sites. A cross-base would typically have a socket to receive the tenon at the foot of a shaft, and the carved circle around this socket is consistent with that interpretation. But Macalister himself raised a second possibility: that the socket and its surround may instead have functioned as a door-socket, a fitting into which a door pivot would turn. The two readings are not easily reconciled. One implies the stone was always seen, always symbolic; the other places it at the threshold, largely hidden beneath the swing of a door, purely practical. The socket is shallow, only five centimetres deep, and its diameter of eight centimetres is on the small side for a cross-shaft, which perhaps lends some weight to the door-socket theory, though nothing has been settled.