What is a "Ganja mbatok mengkureb"?

[A. G. Maisey]

Never heard that expression applied to a keris, but it means a half round shape, ie hemispherical, like a coconut shell cut in half and the cut side put to the ground.(mbathok mengkureb)

Just guessing, maybe they mean that the top of the gonjo is sort of half round or curved, or if applied only to the sirah cecak, that the sirah cecak is half round.