BT BB 6a(31) :אחזיק להורדי ל^א^ אחזיק לכשורי לכשורי אחזיק להורדי‏ : (if ) he had acquired the prescriptive right (to place) reed mats (on his neighbor's wall), he did not have the right for beams; for beams, he had the right for reed mats
See the entire entry for kšūr, kšūrā n.m. beam