The slab sits in the Saint's graveyard on Inis Cealtra, a small island in Lough Derg long associated with early Christian monasticism, and the inscription follows a formula well known from early medieval Irish epigraphy: "Or do," meaning "a prayer for." What makes this particular piece quietly odd is that at least one of the S's in the name is reversed, a quirk of the stonecutter's hand that has survived intact, along with a cross carved at each end of the text.

The slab is just 1.35 metres long and forms the northern edge of what is called a composite grave, meaning a grave constructed from several separate stones rather than a single covering slab. A mortise-like hollow cut into the stone's southern face near its eastern end appears to be connected to how that composite structure was assembled. When the scholar R. A. S. Macalister recorded the graveyard in 1916 to 1917 and produced his plan of the site, he drew this slab as wider and left it without decoration or a catalogue number, suggesting it was either less legible at the time or simply overlooked in the detail of his survey. Later work by Tunney and Manning, published in 2015, identified and documented the inscription more precisely, placing the slab 3.3 metres from the eastern wall of the nearby church known as Teampul na bhFear nGonta and 2.05 metres from the northern wall of the graveyard. The name Thressach is not a common one, and nothing further about the individual is recorded; the inscription is the whole of what remains of them.