Ogham is an early medieval script, used primarily between the fourth and seventh centuries, in which letters are represented by groups of notches and strokes cut along a central stemline, typically running along the edge of a standing stone. That this one is now built sideways into a church wall, functioning as little more than a course of masonry, says something about the shifting priorities of successive centuries.

Clara church contains two such stones, both of red sandstone and both repurposed into the building's fabric. The first serves as the inserted sill of the window in the east gable. This second stone, measuring 1.14 metres by 0.23 metres, sits just above the ground in the external face of the north wall of the nave, immediately to the east of the north doorway. It was discovered only in the 1970s, and Manning and Moore, who examined and documented it, read its partially legible inscription as G[E]LAGN[I] [A]V[I], a formula consistent with ogham memorial stones elsewhere in Ireland, where AVI typically means "grandson of" or "descendant of". The name before it, Gelagni, would be that of the commemorated individual, though several characters remain uncertain or missing. Their findings were published in 1997.

The stone is visible on the exterior of the church wall, which means it can be examined without entering the building. Given its position just above ground level and its horizontal orientation, it is easy to overlook, especially as the inscription runs along what was once the stone's edge rather than across its face. Looking closely at the surface, the notches of the ogham script are cut along the lower arris of the slab.