Trunking 1, in which the first engagement means comprises a part circular bead formed along the free end of each side wall and of radius greater than {HEAD ~ the thickness} of {TAIL ~ said side wall} 
Trunking 1 , in which the first engagement means comprises a part circular bead formed along the free end of each side wall and of radius greater than { HEAD ~ the thickness } of { TAIL ~ said side wall }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL