A new fastener to join Line-8 aluminium profiles mitred at variable angles has been introduced into the Item MB building kit system.
Two basic variants are offered: the Mitre-Fastening Set 8 which comes with a T-slot nut, and is used to fasten a mitred profile to a non-mitred profile; and the Mitre-Butt-Fastening Set 8 which is used to fasten two mitred sections together.
To use the new fasteners, using simple drilling jigs, a cross hole is drilled into the mitred section(s), and a second hole is drilled normal to the mitre-cut face to link up with the first hole. A threaded sleeve is then fitted into the first hole and a threaded pin inserted through the second hole right into the sleeve. Finally a special grub screw is driven into the sleeve, the nose of the grub screw acting on a cup shaped in the pin so as to draw it into the fastener, thus clamping whatever is attached to the other end of the pin. Item have thought carefully about making these fasteners easy to use. Both the threaded sleeve and the mating pin have been specially marked to ensure that alignment of the sleeve and pin is easily achieved, and that the pin is inserted at exactly the correct depth for optimum performance. This ensures that the maximum strength of he fastener is utilised.
In order to make the joint as strong as possible, Item have taken some important steps. Firstly the components are generously sized, to allow a high torque to be applied to the grub screw thus increasing the clamping force. The larger sizing also improves the ability of the fasteners to withstand a small out-of-tolerance positioning of the drilled holes. Secondly, the extra drilling operation ensures that the line of action of the clamping pin is directly perpendicular to the mitred faces, which is the best possible arrangement and maximises the translation of forces between the torque applied, and the resultant clamping force. Thirdly, the geometry of the "cup-and-cone" arrangement has been specially developed to maximise the area of contact and thus reduce excessive stresses.