in viewing fig1 , the complete structure of the height restrictor 28 concept is displayed . the main components are seen to be a bolted mounting base 4 , a mounting post 6 , a head connector 15 , and a restrictor arm 29 . in analyzing the manner in which the components coordinate with each other , fig1 will be visualized part by part , assuming a process of initial construction . we begin the description of the components of the invention with the bolted mounting base 4 , as more clearly shown in fig2 . one of the features of this mounting base 4 is a drilled base plate 2 , containing four base attachment holes 3 . the drilled base plate 2 is designed to be attached , by means of base bolts 27 , to a concrete , wood , or other foundation as shown in fig1 . if conditions warrant , an embedded mounting base 5 , as shown in fig2 ( a ), may be utilized by directly inserting the embedded mounting base 5 into a concrete foundation . placed directly atop either the bolted mounting base 4 , or the embedded mounting base 5 , is a hollow main post 6 to which has been welded a collar 7 . the collar 7 contains two vertically - oriented collar holes 8 , as shown more clearly in fig3 . the main post 6 , collar 7 , and bolted mounting base 4 may be constructed of any mutually compatible geometric lateral cross section . for illustrative purposes , these three components are all depicted as square in shape . the inner dimensions of the collar 7 are of greater length and width than are the outer dimensions of both the main post 6 and the bolted mounting base 4 , as depicted in fig4 . again referring to fig1 , it is observed that the main post 6 and its welded - on collar 7 are shown placed atop the bolted mounting base 4 . the main post 6 and collar 7 are secured in place by means of two collar bolts 9 . higher up the main post 6 there is attached a horizontally - oriented restrictor arm 29 . the restrictor arm 29 serves as the point of contact for vehicles whose upper extremities will collide with an overhanging obstacle should the vehicle continue past the location of the height restrictor 28 . the height restrictor 28 comprises a head assembly 10 and a head assembly housing 18 . referring to fig5 , a cutaway view of the head connector 15 , included a welded - on hollow metal sphere 22 is presented . in a similar manner as the design of the collar 7 dimensions , the inner dimensions of the head connector 15 are such as to allow the head connector 15 to fit comfortably over the outer dimensions of the main post 6 . two connector holes 25 , one beneath the other , are drilled into one outer wall of the head connector 15 . for each connector hole 25 , a connector nut 16 , with a threaded hole of the same inner diameter as its paired connector hole 25 , is co - axially centered with the connector hole 25 and then said connector nut 16 is welded onto the wall of the head connector 15 . during final assembly of the height restrictor 28 , connector bolts 17 are rotated into the connector nuts 16 , through the connector holes 25 , and tightly fitted against the outer wall of the main post 6 . it is at this point of the assembly that the height restrictor 28 may be adjusted up or down along the length of the main post 6 to match the required alerting height of the overhead obstacle . as further seen in fig5 , the hollow sphere 22 is welded 23 to the outer surface of the wall of the head connector 15 opposite the connector nuts 16 . there is also depicted a circular opening 24 drilled through the hollow sphere 22 so as to allow insertion of a passing link chain 11 . the passing link chain 11 is welded to the inner wall of the hollow sphere 22 as more clearly depicted in fig6 . fig6 presents a full view of the head assembly 10 which comprises the primary functional component of the inventive concept . plan views of both a longitudinal cross - section of the head connector 15 , and a view of the head assembly 10 are shown . scanning fig6 from left to right , there is observed the head connector 15 , onto which is welded 23 the hollow sphere 22 . within the hollow sphere 22 , at its tangential point to the head connector 15 , one end of the passing link chain 11 is welded . a circular opening 24 has been drilled through the hollow sphere 22 to allow the passing link chain 11 to pass freely through and to oscillate , as necessary , in a variety of directions , as may be caused by a nudge from a vehicle . the passing link chain 11 , at its distal end , connects , by means of an s - hook 12 , to an extension spring 13 . on the opposite end of the extension spring 13 a second s - hook 12 ( a ) is engaged . the second s - hook 12 ( a ) is inserted through a hole at the proximate end of an elongated threaded rod 14 . at the distal end of the threaded rod 14 a retaining nut 21 is rotated into position to secure a head assembly housing 18 , said housing functioning to cover the entirety of the head assembly 10 . fig7 depicts the head assembly housing 18 , a reducer bushing 19 , and a housing end cap 20 . the reducer bushing 19 and the housing end cap 20 may be glued onto their respective ends of the head assembly housing 18 . the specific embodiment presented in fig7 and fig7 ( a ) shows the head assembly housing 18 as a circular tube . other embodiments may utilize the head assembly housing 18 in a square longitudinal cross - section , or in any other geometric shaped cross - section . the housing end cap 20 contains a center - positioned hole to allow a short protrusion of the distal end of the threaded rod 14 . the retaining nut 21 is then rotated onto the threaded rod 14 and securely tightened against the end cap 20 . in its operational environment , once the mounting base 4 and main post 6 of the height restrictor 28 are assembled and securely mounted at the required location , a calculation is made as to the height of the associated overhanging obstruction to which an alert is desired . the head assembly 10 and housing 18 are united with the head connector 15 by the final step of securing the retaining nut 21 against the end cap 20 , thus forming the restrictor arm 29 . the head connector 15 is next positioned over the perimeter of the main post 6 and positioned vertically at a linear measurement corresponding to the desired alert height . the head connector 15 is then securely fastened into place by means of head connector bolts 17 inserted through the head connector 15 and securely fastened against the main post 6 . as an over - height vehicle approaches the height restrictor 28 and contact is made with the restrictor arm 29 , the extension spring 13 within the hollow sphere 22 allows the restrictor arm 29 to move forward , aft , up , or down , or any combination of these directions , as an input force is received from the vehicle . thus , the driver , or any person positioned to observe the approach of the vehicle , is alerted to the probability of a collision with the overhanging obstruction . once the alert is observed and the driver makes a corrective re - positioning of the vehicle , the restrictor arm 29 is pulled back to its original horizontal position by retraction of the extension spring 13 and the centering effect of the reducer bushing 19 , due to the inherent seating of the reducer bushing 19 against the hollow sphere 22 . the design of the height restrictor 28 also permits the inclusion of internal wiring which may supply a low - voltage source to an aural warning system and / or an illuminated light , either on the height restrictor 28 or at a nearby manned station or checkpoint . this inventive concept may be disassembled and re - located to any suitable location , depending on the permanency of its mounting foundation . it is recognized that one knowledgeable and skilled in the art , has the capability to design or produce similar , or other embodiments of the disclosures presented herein . however all such variations , alterations , or modifications are entirely conceivable as being within the intent and scope of the present inventive concept .