You are right !! i figured it out that one.... the thing is that in order to fasten the angled bracket Or the straight one you still need a plastic pulley to tighten it to the gland ... the top part of the gland tightens to the plexiglass tube and the bottom pulley - that is missing ----tightens the angled piece.....my kit did not have any ( and i have ordered 2 of these kits just to be sure that i was going to assemble it right ) ..... another thing is that the hole of the angled piece is a bit small and cannot fit into the gland.... i iused a small file to open the hole a bit in order to prevent damaging the threads of the gland...
if one is missing this plastic pulley there are plenty of them at electric supply stores

cheers
Christos