That is a female plug.
Hole in the center = socket - female.
Don't feel bad: a lot of people are confused by coaxial power barrel connectors.
According to the specs, the plug has an outer diameter of 5.5 mm and the matching male jack has an inner pin with a 2.5 mm diameter.
looking for a panel mount counterpart
Digikey offers these 5 parts: panel-mount male coaxial barrel power jack, 2.5 x 5.5 mm.
But in another vendor here, they mention center pin:
Center-pin length: 11 mm
What they really mean is "barrel length: 11 mm". That is the length of the contact area of the plug: the distance from the tip of the plug to its base against the plastic mold.