fig1 a shows a simplified representation of a printhead module 106 mounted in a mounting structure 102 . the printhead module is typically formed of silicon and is relatively thin , for example , having a thickness in the range of approximately 0 . 3 to 2 . 0 millimeters . the exposed planar face shown in fig1 a of the printhead module 106 is the nozzle face and includes an array of nozzles ( not shown ) from which a printing fluid can be ejected . the printing fluid can be ink , but also can be other liquids , for example , electroluminescent material used in the manufacture of liquid crystal displays or liquid metals used in circuit board fabrication , or biological fluid . fig1 b shows the mounting structure with the printhead module 106 removed . in this implementation , the mounting structure includes a central portion 105 flanked on two opposing sides by winged portions 104 . a receiving surface 107 for the printhead module 106 is included on an end of the central portion 105 . other configurations of mounting structure are possible , and the one shown is but one example . the printhead module 106 is mounted on the receiving surface 107 in the mounting structure 102 between the two opposing winged portions 104 . in the mounting structure configuration shown , the winged portions 104 are configured with apertures 108 , such that the wing portions can be attached to a fluid ejection system where the mounting structure is supported by a frame attached to the winged portions 104 by connecting members passing through the apertures . it should be understood that the mounting structure can be attached to the fluid ejection system in other manners , for example , by an adhesive , and including apertures in the wing portions is optional . typically , two or more printhead modules and mounting structures are mounted to such a frame . the nozzles included in each printhead module are aligned relative to one another when mounting to the frame , so as to provide a larger array of nozzles with consistent spacing between neighboring nozzles . to provide for some manipulation of the printhead module 106 when mounting the mounting structure 102 into a fluid ejection system , the exposed edges 110 and 112 of the printhead module 106 extend past the edges of the winged portions 104 . fig2 shows two printhead modules mounted in adjacent mounting structures and positioned adjacent one another , for example , as they may be positioned when mounted within the frame of a fluid ejection system . although exaggerated for illustrative purposes , there is typically a gap “ g ” between the edges of the adjacent printhead modules and a larger gap “ h ” between the edges of the corresponding mounting structures . the gap “ h ” allows the relative positions of the printhead modules to be adjusted in one or more directions , for example , in the x direction or y direction , and / or rotationally in the z direction . the relative positions of the printhead modules , and accordingly the nozzles included therein , can thereby be adjusted to provide for precise nozzle alignment as between neighboring printhead modules before attaching the corresponding mounting structures to the frame of the fluid ejection system . a difficulty with the mounting structure 102 shown in fig1 b is illustrated in fig3 a . because the edges 110 and 112 of the printhead module 106 extend past the winged portions 104 of the mounting structure , they are vulnerable to damage during assembly of the printhead module into a fluid ejection system . fig3 a shows a view of the configuration shown in fig1 a resting on end against a surface 112 , which could occur during the assembly process . the entire weight ( or a substantial portion thereof ) of the printhead module / mounting structure assembly can end up on the exposed edge 110 of the printhead module . because the printhead module 106 is formed from a relatively thin layer of silicon , the exposed edge 110 is prone to damage . the printhead module 106 can be an expensive element in the assembly and if damaged , may be rendered completely unusable . accordingly , preventing damage to the printhead module 106 and the exposed edges 110 and 112 is important to avoid unnecessary manufacturing expenses and delays . fig3 b shows a partial view of a printhead module 306 mounted within a mounting assembly including winged portions 304 . the winged portions 304 each include on their edges adjacent the exposed edges of the printhead module ( e . g ., edge 310 ) features that extend beyond the exposed edges of the printhead module . in the implementation shown , the features are nubs 303 that extend past the exposed edge 310 of the printhead module 306 . as such , when the printhead module / mounting structure assembly is resting against a surface 112 , as shown , the weight of the assembly is on the nubs 303 rather than the exposed edge 310 of the printhead module 306 . the edge 310 is less likely to come into contact with other surfaces and less vulnerable to damage . dimples 305 are also provided along the edges of the winged portions 304 for allow a recess for the nubs 303 to position in when multiple mounting structures are arranged adjacent one another in a fluid ejection system , as is described further below . fig4 a shows a perspective view of the printhead module 306 mounted in the mounting structure 302 . fig4 b shows the mounting structure 302 with the printhead module 306 removed . in this implementation , the mounting structure 302 includes the winged portions 304 attached to a central portion 309 , the entire length of which is not shown . a receiving surface 307 for the printhead module 306 is provided on an end of the central portion 309 between the winged portions 304 . apertures 308 are included in the winged portions 304 to attach the mounting structure 302 to a frame of a fluid ejection system . such apertures 308 are optional , and other techniques can be used to attached the mounting structure to a fluid ejection system , e . g ., adhesive . the mounting structure can have other configurations , as long as the edges of the mounting structure ( referred to herein as the “ featured edges ”) adjacent the exposed edges 310 , 312 of the printhead module 306 include features that extend beyond the exposed edges 310 , 312 , so as to provide protection from damage . that is , the mounting structure may not necessarily be configured to include winged portions 304 extending from a central portion 309 , or may have a differently shaped cross - section than shown . however , whatever the configuration of the mounting structure 302 , the printhead module 306 is positioned within the mounting structure such that the featured edges of the mounting structure are provided on either side of the exposed edges of the printhead module , and the featured edges include features as described above . referring again to fig4 a and 4b , in the implementation shown , the nubs 303 and dimples 305 extend the entire thickness of the winged portions 304 . however , in other implementations , the nubs 303 and dimples 305 extend only partially the thickness of the winged portions 304 . in the implementation shown , there is one nub and one dimple on each edge of the winged portion 304 and they are arranged symmetrically about a central longitudinal axis of the receiving surface 307 . in some implementations , the nubs and dimples can be arranged asymmetrically about the central longitudinal axis as shown in fig4 c , i . e ., as a mirror image about the central longitudinal axis . an advantage of this configuration , is that the mounting structure has a “ right ” and “ wrong ” way of being mounted onto the frame of a fluid ejection system , in order that the nubs of the mounting structure mate with the dimples of a neighboring mounting structure . that is , the mounting structure cannot be inadvertently mounted backwards ( i . e ., rotated by 180 °) onto the frame , which can be important in implementations where the printhead module has a “ right ” and “ wrong ” orientation . in some implementations , additional nubs and dimples can be included . it should also be understood that in other implementations , the features extending beyond the exposed edges of the printhead module can have a configuration other than a nub , for example , can have squared corners , or otherwise . the nubs 303 and dimples 305 included in the winged portions 304 of the mounting structure 302 are configured so as not to interfere with the relative positioning of neighboring printhead modules 306 . that is , the nubs 303 and dimples 305 are positioned and dimensioned to allow for a nub 303 to nest within a corresponding dimple of an adjacent mounting structure , without dictating or interfering with the relative position of the printhead modules mounted within the two mounting structures . fig5 shows an enlarged view of a portion of a first mounting structure having a winged portion 304 positioned adjacent to a second mounting structure having a winged portion 314 . for illustrative purposes , the two mounting structures are affixed into a frame of a fluid ejection system and the relative positioning of the printhead modules 306 and 320 mounted therein has been determined so as to align the nozzles of the printhead modules 306 and 320 relative to each other . the nub 303 has a depth “ b ” and is nested within a dimple 316 of depth “ d ” formed in the second mounting structure . the outer surface of the nub 303 does not need to contact the inner surface of the corresponding dimple 316 when the first and second mounting structures are attached to the frame of the fluid ejection system . as is shown in fig5 , a gap 318 ( which is exaggerated for illustrative purposes ) can exist between the surfaces of the nub 303 and dimple 316 . if the surfaces of the nub 303 and the dimple 316 do come into contact , this contact can dictate the final position of the first and second mounting structures , and therefore the relative position of the printhead modules 306 and 320 mounted therein . preferably , the relative position of the printhead modules 306 and 320 is determined by alignment of the nozzles included in each printhead module , rather than the nubs and dimples of the mounting structures . accordingly , the nubs and dimples can be configured and dimensioned to satisfy the relationship below , so as to prevent their interfering with the positioning of the printhead modules : x 1 = the distance by which the exposed edge 310 of the printhead module 306 extends past the edge of the winged portion 304 ; g = the gap between the printhead modules 306 and 320 ; x 2 = the distance by which the exposed edge 322 of the printhead module 320 extends past the edge of the winged portion 314 ; additionally , x 1 + x 2 & lt ; b . the gap “ g ” between the printhead modules 306 and 320 can be determined by nozzle alignment between the two printhead modules 306 , 320 , and therefore can vary from instance to instance . however , a range that the gap “ g ” may fall within can be estimated and the minimum value in the range can be used in the above relationship to determine a value for the depth b of the nub or the depth d of the dimple . in the implementation shown in fig3 b , 4 a and 5 , the printhead module 306 is configured having a rectangular shape . in other implementations , the printhead module can be configured with a different shape . in fig6 , an example is shown where the printhead module 330 is a non - rectangular parallelogram mounted within a mounting structure having a generally rectangular cross - section ( other than the nubs and dimples included on the edges of the winged portions 304 ). in other implementations , the mounting structure can have a cross - section shaped other than as a rectangle . referring to fig6 , the exposed edges 332 and 334 of the printhead module 330 are angled relative to the featured edges of the winged portions 304 of the mounting structure . however , the nubs 303 still extend past the outermost corners of the edges 332 and 334 , and thereby provide protection for these vulnerable edges , e . g ., during the assembly process . in some implementations , a printhead module 330 having a non - rectangular parallelogram configuration as shown has an array of nozzles formed therein that are aligned parallel to the edges 332 and 334 , and the printhead module 330 moves in the y direction relative to a substrate being printed on , i . e ., moves in a direction parallel to the featured edges of the winged portions . other implementations are possible , and this is but one example . referring to fig7 a and 7b , for illustrative purposes , an example printhead module 700 is shown . a cross - sectional view of a portion of the printhead module 700 is shown and fig7 a shows the upper section in an exploded view . the printhead module 700 is but one example of a printhead module that can be mounted within a mounting structure as described above and is not a limiting example ; other configurations can be used . in the example shown , the printhead module 700 includes a substrate 708 in which a plurality of fluid flow paths are formed ( only one flow path is shown ). the printhead module 700 also includes a plurality of actuators to cause fluid ( e . g ., ink ) to be selectively ejected from the flow paths . thus , each flow path with its associated actuator provides an individually controllable mems fluid ejector . in this implementation of a printhead module , an inlet fluidically connects a fluid supply ( not shown ) to a substrate 708 . the inlet is fluidically connected to an inlet passage 110 through a channel ( not shown ). the inlet passage 710 is fluidically connected to a pumping chamber 712 . the pumping chamber 712 is fluidly connected to a descender 716 terminating in a nozzle 718 . the nozzle 718 can be defined by a nozzle layer 720 attached to the substrate 708 . the membrane 704 is formed on top of the substrate 708 in close proximity to the pumping chamber 712 , e . g . a lower surface of the membrane 104 can define an upper boundary of the pumping chamber 712 . the actuator 702 is disposed on top of the membrane 704 , and an adhesive 703 is between the actuator 702 and the membrane 704 . in the example shown , the actuator 702 is a piezoelectric actuator and includes a piezoelectric layer 731 positioned between a drive electrode 730 and a ground electrode 732 . a voltage differential is applied across the drive and ground electrodes 730 , 732 to activate the piezoelectric layer 731 , causing a deflection of the piezoelectric layer 731 and the member 704 . in other implementations , a different configuration of actuator can be used , for example , a thermal actuator . it should be understood that in other implementations , the membrane 704 can be excluded , and the piezoelectric layer 731 itself can form a boundary of the pumping chamber 712 . in implementations where the printing fluid can corrode the piezoelectric material , the surface forming the boundary of the pumping chamber can be protected by a protective layer , for example , a polyimide layer such as upilex ® or kapton ®. in operation , fluid flows through the inlet into the substrate 708 and through the inlet passage 710 . fluid flows up the inlet passage 710 and into the pumping chamber 712 . when the actuator 702 above the pumping chamber 712 is actuated , the actuator 702 deflects the membrane 704 into the pumping chamber 712 . the resulting change in volume of the pumping chamber 712 forces fluid out of the pumping chamber 712 and into the descender 716 . fluid then passes through the nozzle 718 , provided that the actuator 702 has applied sufficient pressure to force a droplet 719 of fluid through the nozzle 718 . the droplet 719 of fluid is ejected and can then be deposited on a substrate . the use of terminology such as “ front ” and “ back ” and “ top ” and “ bottom ” throughout the specification and claims is for illustrative purposes only , to distinguish between various components of the printhead module and other elements described herein . the use of “ front ” and “ back ” and “ top ” and “ bottom ” does not imply a particular orientation of the printhead module . similarly , the use of horizontal and vertical to describe elements throughout the specification is in relation to the implementation described . in other implementations , the same or similar elements can be orientated other than horizontally or vertically as the case may be . a number of embodiments of the invention have been described . nevertheless , it will be understood that various modifications may be made without departing from the spirit and scope of the invention . accordingly , other embodiments are within the scope of the following claims .