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