from the perimeter, and the cap fitting between segments in the head of the bolt and locking with a twist-in motion to capture a rod in the opening. A hold-down set screw threads through a central opening in the cap and tightens down against the rod to clamp the rod firmly in place. The closing and clamping may each be effected by a driver tool that operates along the axis of the assembly and requires little or no side clearance to rotate either the cap or the set screw. In the case of the external, twist-on cap, the limited degree of rotation allows the cap to also include slots through the cap to accommodate reduction tabs extending upwardly from the underlying screw or anchor member. The quick-twist closureon re-watching italian writer/director dario argento's much lauded murder mystery tenebrae , i was struck more than anything else by how many sins he commits as a storyteller and manages to get away with . 
in emphasising style over matters of plot argento is somewhat notorious in cult film circles , but some aficionados still praise tenebrae as the greatest of his " giallo " murder mysteries . 
while it's certainly not perfect , repeated viewings reveal it to be nonetheless a densely plotted and terrifically stylish thriller . 
the story follows a promotional visit to rome by famous american mystery novelist peter neal ( anthony franciosa ) where he discovers that a serial killer is on the loose inspired by his latest book " tenebrae " .