process entails besides a huge manual labour a particular attention to the grating being parallel and perpendicular compared with the span which as it often happens especially in non recent buildings can be geometrically not regular said system which is at present the only one known has also the relevant drawback of being very expensive and needing the work of a skilled worker in addition once the grating has been fitted in the aforesaid way it 39 s difficult to remove it from its position and place it elsewhere and even if one decides to do it anyway it 39 s necessary to destroy the wall in the part where the hinges have been walled the present invention aims at eliminating the above mentioned and other drawbacks supplying a fitting device essentially consisting of two telescopic elements which support both the building part and the security grating equipped with register elements that if rotated let the two sides of the telescopic parts lengthen so that joining the ends of the span they show the exact position of tracer for the drilling another facilitation is given by the eccentric construction of the supports provided with this device which will avoid possible linearity errors in.