Without knowing the exact context, "χερούλι" is a "handle" (of a door, of a cupboard door, of a suitcase). From what I understand, what you mean to say is the holding on to the railing (κάγκελο) or bannister (κουπαστή) of a staircase.
Also, do you mean "Πιάσε" or "Πιάσου από"?
Πιάσου από το κάγκελο/τα κάγκελα = Hold on to the railing