The roof element of the 10" velux rigid sun tunnel has already been fitted over the new stairs to the loft conversion. My part is to fit the internal sections. I have fitted the upper elbow to the roof element. The lower elbow will fit into the ceiling disc when it is fitted into a new ceiling - still to be attached. Problem: the 24" extension piece is too long to fit betwen the two elbows. I tried cutting the extension piece to about 20" but it is very difficult. The two elbows might just overlap each other - should I open one of the rivets to make them fit into each other?