so as to have have two end portions one end portion can connect with moving block 3 and can include parallel side portions 5a and 5c side portions 5a and 5 can terminate with a perpendicular side portion 5b side portion 5a can extend longitudinally to the right in the guide rail until side portion 5a reaches the right end of sliding block 3 at the right end of sliding block 3 a side portion 5d extends towards the adjacent guide rail 1 perpendicular to side portion 5a thereby expanding the width of release 5 side portion 5d can terminate near the guide rail 1 at which point side portion 5e can extend out to the right in the direction toward the engaging and disengaging lever 6 side portions 5c and 5e preferably extend essentially parallel to one another and terminate with approach bevel 7 side portion 5c also may have a small lip or flange 7a toward its terminal end this bevel 7 and flange 7a being designed for interaction with lever arm 16 of the engaging and disengaging lever 6 as the preferred embodiment makes clear in addition to the sliding blocks all of the mechanical equipment of the closing mechanism located inside the guide rail 1 and thus also the engaging and disengaging lever 6 are invisible to the observer when the two panels 21.