fig1 shows a portion of one vertical side frame of a sash window frame assembly comprising a frame portion 10 defining a pair of vertical channels 11a and 11b ( shown only in part ), support portions 20 ( only one of which is shown ) slidably movable in one of said channels 11a and 11b respectively and operatively supporting , in use , a movable frame mounting panes of glass ( not shown ). the weight of the movable frame is counterbalanced by eight coiled ribbon springs ( four at each side of the frame -- only four are shown in fig1 ). the four springs shown in fig1 springs 30 , 32 , 34 and 36 are mounted to rotate about pivots 30a , 32a , 34a and 36a respectively . each has a coiled ribbon body portion and a free end terminating in a tongue 30b , 32b , 34b and 36b respectively . three of the springs 30 , 34 , 36 are identical in size and in the length of their tongues . each has a tongue about 1 . 5 times the diameter ` d ` of a coiled ribbon spring body portion ( all are of approximately the same diameter ) and the springs are each mounted on a respective reel ( see fig2 ) for rotation about their respective axes . a portion of the reel for spring 30 is shown cut - away in fig1 to reveal a portion of the ribbon body portion 30c of that spring and the free end 30d thereof . the spring 32 is generally similar to the other springs except that it has a tongue about 3 . 5 times the diameter ` d ` of a coiled ribbon spring body portion . the tongues of spring 34 and 36 are provided at their ends with engagement means each provided by a narrowed region of hook shape 34e , 36e . spaced from that first engagement means on the tongue of spring 36 is a slot 36f which provides second engagement means for the reception of first engagement means 34e of spring 34 . the distance between the first and second engagement means on spring 36 is approximately equal to one coiled ribbon spring diameter ` d `. the hooked end 36e of spring 36 is engaged in the support member 20 which is provided with a slotted recess to engage the same . similarly , the tongues of spring 30 and 32 are provided at their ends with first engagement means 30e , 32e . engagement means 32e of spring 32 are engaged in a recess in the support member 20 and the tongue of that spring is also provided with second engagement means comprising a slot 32f which receives the hooked end 30e of spring 30 . springs 30 and 32 act in concert by virtue of their engagement and rotate in the same sense , as do springs 34 and 36 , which rotate in the same sense but opposite to that of springs 30 and 32 . in fact springs 30 and 34 also have second engagement means ( springs 30 , 34 and 36 being identical ) but the second engagement means of springs 30 and 34 are not , in the arrangement shown , used . it will be seen that insertion of the springs into their position , upon assembly of the arrangement is quite simple . spring 36 is slid into the channel 11a and moved up to the support member 20 until its hooked end 36e is received in the corresponding receptacle . pivot 36 is then established by means of a screw ( not shown ) and spring 34 is then slid into the channel 11a with the hooked end 34e being threaded between spring 36 and a wall 12 of the channel 11a . it will be seen that the hooked end 34e will , by virtue of the springiness of the tongue 34b , locate in slot 36f whereupon the pivot 34a of spring 34 can also be established by means of a screw ( not shown ). springs 32 and 30 are then inserted in like manner . it will be found in practice that the arrangement also enables the assembly to be taken to pieces should this be required e . g . for the replacement of a damaged spring . the arrangement of springs shown in fig1 is only one example of how the invention may be employed advantageously . fig3 shows a schematic arrangement of springs which is in an alternative to the arrangement shown in fig1 . in fig3 there are three springs 60 , 62 and 64 having tongues of the same length and fourth spring 66 which has a tongue of shorter length . in that arrangement the tongues of the lower - most spring 66 and the second lower - most spring 64 are attached to the support member 50 . the tongue length is approximately 2 . 5 times ` d ` in respect of the three identical springs and approximately 1 . 5 times ` d ` in respect of spring no . 66 . the spacings between the first and second engagement means for springs 60 , 62 and 64 is approximately 2 . 0 times ` d ` and for spring 66 approximately 1 . 0 times ` d ` the second engagement means of springs 62 and 60 are not used in the arrangement shown in fig3 . the arrangement shown in fig3 a comprises four identical springs 60 &# 39 ;; 62 &# 39 ;; 64 &# 39 ;; and 66 &# 39 ;; each having the same tongue length and each identical to spring 36 shown in fig1 . all the springs rotate in the same sense and the first engagement means ( hook ) of the uppermost spring engages the second engagement means ( slot ) of the spring beneath it and so on . the thickness of the coiled ribbon springs in fig4 - 6 has been emphasized relative to their width . fig4 shows a free end portion of a coiled spring of the type used in the embodiment of fig1 to 3 and 3a . the first engagement means comprises a hooked end 70 , of narrowed width . the second engagement means comprises a lateral slot 72 cooperable with a hooked end first engagement means of a second coiled ribbon spring ( not shown but either having an identical free end portion to that shown in fig4 or being identical thereto ). the spring end shown in fig4 has the advantage that it is easy to engage two similar springs together , the hook of one spring riding along the back 74 of the first spring until engaged in slot 72 . fig5 shows an alternative end formation for a coiled ribbon spring of a type capable of being used in the arrangement of fig1 - 3 , and comprises first engagement means 80 provided by a ` t `- shaped end formation ( which is not hooked ), the second engagement means 82 comprising a ` t `- shaped slot , larger , but shaped similarly to the first engagement means . it will be readily apparent how two springs of the type shown in fig5 may be engaged with each other . fig6 shows a further end formation wherein the first engagement means comprises two laterally spaced hook formations 90 , and the second engagement means comprises a pair of indents 92 . it will be readily apparent that any suitable engagement means will be appropriate in performing the invention and not only the hook and slot arrangement described . the spring according to the invention may be used in assemblies of two , three , four or more within the limitations of space available according to need , with more than two springs working in concert if required .