for purposes of illustration , fig1 shows an endoscopic camera arrangement 10 , including a scope assembly 11 which may be utilized in endoscopic procedures , for example . the scope assembly 11 incorporates an endoscope or scope 12 which is coupled to a camera head 13 by a coupler 14 located at the distal end of camera head 13 . camera head 13 incorporates well - known circuitry , such as a charge - coupled device ( ccd ) or a complementary metal oxide semi - conductor ( cmos ), for acquiring color video image data of internal features of the body through one or more lenses within the scope 12 . light is provided to the scope 12 by a light source 14 a via a light conduit 15 , such as a fiber - optic cable . the camera head 13 is coupled to a camera control unit ( ccu ) 17 by a transmission cable 18 . operation of the camera arrangement 10 is controlled , in part , by ccu 17 . cable 18 conveys video image data from the camera head 13 to the ccu 17 and conveys various control signals bi - directionally between the camera head 13 and the ccu 17 . in one embodiment , the image data output by the camera head 13 is digital , in which case cable 18 may be firewire , a universal serial bus ( usb ) or another type of high - speed digital interface . a control or switch arrangement 20 ( fig2 ) is provided on the camera head 13 and allows the user to manually control various functions of the camera arrangement 10 . these camera functions may also be controlled by voice commands using a voice control unit 23 , which control unit 23 is coupled to ccu 17 . voice commands are input into a microphone 24 mounted on a headset 25 worn by the surgeon and coupled to the voice control unit 23 . a hand - held control device 26 , such as a tablet with a touch - screen user interface or a pendant , may be coupled to the voice control unit 23 as a further control interface . in the illustrated embodiment , a dvd recorder 27 and a printer 28 are also coupled to the ccu 17 . additional devices , such as an image capture and archiving device , may be included in arrangement 10 and coupled to ccu 17 . video image data acquired by camera head 13 and processed by ccu 17 is converted to images , which can be displayed on a monitor 29 , recorded by recorder 27 , and / or used to generate static images , hard copies of which images can be produced by printer 28 . with reference to fig3 - 6 , camera head 13 includes a housing 30 defined by a generally tubular housing wall 31 defining a hollow interior 32 . interior 32 opens distally through an opening 33 which cooperates with coupler 14 , and sidewardly through a bore or opening 34 which extends completely through housing wall 31 and mounts therein control or switch arrangement 20 . bore 34 is defined by an annular terminal edge portion of housing wall 31 having multiple stepped sections or portions as described below . housing wall 31 includes an annular flange 35 having an inner surface 36 oriented generally transverse to a longitudinal axis a of scope 11 ( which axis a is generally parallel to a horizontal plane of bore 34 ), and generally parallel to a central axis b of bore 34 ( which axis b is oriented transversely to axis a ). surface 36 defines a radially innermost portion 38 of bore 34 with respect to scope axis a , and in the illustrated embodiment portion 38 has the smallest diameter of all of the sections of bore 34 . surface 36 is joined to a flat annular surface 39 which is generally parallel to scope axis a and generally perpendicular to bore axis b , which surface 39 , in turn , is joined to a further surface 40 of housing wall 31 . surface 40 is essentially perpendicular to axis a and essentially parallel to axis b . surfaces 39 and 40 are oriented transversely to one another , and in the illustrated embodiment together form a right angle . further , surface 40 is located axially outwardly from surface 36 with respect to scope axis a , and is generally parallel to surface 36 , so as to define an intermediate portion 42 of bore 34 having a larger diameter than adjacent bore portion 38 . an upper extent of surface 40 is joined to an annular sealing surface 44 which protrudes radially relative to scope axis a and is joined to a flat annular surface 45 . with respect to axis a , surface 45 is located radially inwardly from surface 44 and axially outwardly therefrom . surface 45 is joined to a wall surface 48 which is generally parallel to surface 40 and is located axially outwardly ( axis a ) therefrom so as to define a further bore portion 50 of a larger diameter than adjacent bore portion 42 . surface 48 , surface 45 and an outer surface of sealing surface or projection 44 together define an annular recess or notch 49 located immediately adjacent sealing projection 44 , and projecting radially inwardly relative thereto with respect to axis a . surface 48 is joined to a flat annular surface 52 which adjoins an annular housing wall surface 53 located axially outwardly from wall surface 49 ( axis a ) and generally parallel thereto so as to define a further bore portion 60 of a greater diameter than adjacent bore portion 50 , but of a lesser radial dimension than bore portion 50 ( axis a ). bore portion 60 joins to an outermost bore portion 61 defined by an annular housing surface 63 located axially inwardly ( axis a ) from adjacent housing surface 53 such that housing wall 31 defines an outer flange 65 which overhangs bore portion 60 so as to form a retaining lip therearound . outermost bore portion 61 is the radially outermost part of bore 34 ( axis a ). in the illustrated embodiment , flange 65 is annular . however , it will be appreciated that flange 65 may be embodied by a plurality of flanges or projections located about the periphery of bore 34 , or only a single flange of an adequate circumferential dimension may be provided along a portion of the outer periphery bore . with reference to fig5 and 6 , in the illustrated embodiment , flange 65 angles upwardly as same projects radially inwardly with respect to and towards axis b , and thus defines a slightly upwardly inclined inner surface 67 which is oriented at an angle in the range of about 15 - 20 degrees relative to axis a . turning now to control arrangement 20 , and with reference to fig3 and 11 , same includes a membrane switch 70 having outer and inner members 71 and 72 . outer member 71 mounts thereon a pair of switch contact pads 73 and 74 which are normally in the open position . outer member 71 is generally planar and has an outer periphery sized so as to relatively snugly seat within bore portion 42 of housing bore 34 so that outer member 71 rests atop housing flange 35 , while inner member 72 projects into innermost bore portion 38 . membrane switch 70 contains suitable circuitry electrically connected to the appropriate components within camera head 13 such that the appropriate control commands are carried out when contact pads 73 and 74 are actuated , as discussed further below . control arrangement 20 additionally includes an actuator or keypad 80 , as shown in fig3 , 7 and 11 . keypad 80 has a base member 81 which surrounds and is joined to a pair of raised buttons 82 and 83 which project outwardly from base member 81 . buttons 82 and 83 have respective upper or outer surfaces which include indicia thereon corresponding to various control functions of camera head 13 . in the illustrated embodiment , the buttons 82 and 83 respectively include the letters “ p ” and “ w ” thereon , which are representative of “ picture ” and “ white balance ” functions of camera head 13 . base member 81 of keypad 80 has an outer annular edge portion 85 which surrounds buttons 82 and 83 , and an inner web portion 86 disposed between buttons 82 and 83 . edge portion 85 and web portion 86 are generally coplanar with one another , and in the illustrated embodiment are integrally formed as one - piece with buttons 82 and 83 . web portion 86 includes a lower or inner generally flat surface 87 , and outer edge portion 85 includes a lower or inner surface 89 coplanar with surface 87 . outer edge portion 85 defines an annular lip 88 which projects downwardly or inwardly from surface 89 . buttons 82 and 83 each have respective projections 90 and 91 which are cantilevered downwardly or inwardly and define respective lower or inner surfaces 92 and 93 which are generally planar and coplanar with one another . in the illustrated embodiment , keypad 80 is formed as a one - piece component constructed of an elastomeric and resilient material . with reference to fig1 , keypad 80 is located within bore portion 50 so that lip 88 of base 81 engages within notch 49 and against sealing projection 44 and so that lower surface 89 of base edge portion 85 and lower surface 87 of web 86 seat on the upper surface of membrane switch 70 . further , the lower surfaces 92 and 93 of actuating projections 90 and 91 of keypad 80 are spaced slightly upwardly from the respective contact pads 73 and 74 of membrane switch 70 . as shown in fig1 , when keypad 80 is assembled to housing 31 atop membrane switch 70 , actuating projections 90 and 91 are aligned with contact pads 73 and 74 . control arrangement 20 additionally includes a cover plate 100 as shown in fig3 and 8 . cover plate 100 is shaped to cooperate with keypad 80 , and includes a planar base wall 101 which defines therein openings 102 and 103 which extend completely through base wall 101 and are shaped to correspond with the outer peripheries of buttons 82 and 83 . buttons 82 and 83 extend upwardly or outwardly through the respective openings 102 and 103 in the assembled condition of control arrangement 20 . as shown in fig1 , cover plate 100 seats atop base 81 of keypad 80 within bore portion 50 , with buttons 82 and 83 of keypad 80 located within the respective openings 102 and 103 . with reference to fig3 and 10 , control arrangement 20 additionally includes a retainer clip 110 defined by an elongated body 111 generally having an elliptical shape . clip body 111 is of a split - ring construction , and thus has a pair of terminal or free ends 112 which are spaced sidewardly from one another to allow compression of clip 110 . as shown in fig1 , the free ends 112 have chamfers 113 which assist in removing clip 110 from housing 30 . additionally , at the side of clip 110 diametrically opposite from ends 112 , body 111 projects inwardly so as to define a recess 114 which aids in installation of clip 110 by allowing easier compression thereof . referring to fig1 , with membrane switch 70 , keypad 80 and cover plate 100 assembled within bore 34 of housing 31 , these components of control arrangement 20 are secured within housing 30 via retainer clip 110 . specifically , according to one assembly method , retainer clip 110 is compressed by applying pressure to the opposite sides of body 111 located between ends 112 and recess 114 , so that clip 110 can be inserted into and pass through outermost bore portion 61 over flange 65 . once clip 110 has cleared surface 63 of flange 65 which defines bore portion 61 , the pressure on clip 110 is removed so that the clip 110 resiliently returns to its normal or at rest configuration ( as shown in fig1 ) and moves into bore portion 60 atop cover plate 100 . in this regard , the angled surface 67 of flange 65 serves to guide the clip 110 downwardly during insertion or installation so that same seats within bore portion 60 and is brought into engagement with the cover plate 100 . with clip 110 in place within bore 34 of housing 31 , clip 110 prevents dislodgement of the underlying components of the control arrangement 20 , and also compresses keypad 80 and maintains lip 88 of keypad 80 in notch 39 and in contact with surfaces 48 , 45 and 44 of housing 31 so as to effectively create a fluid - tight seal between the external environment and the components internal to housing 31 , including membrane switch 70 and the electronic circuitry and other components located within housing 30 of camera head 13 . in the illustrated embodiment , the dimensions of flange 88 of keypad 80 are somewhat larger than the dimensions of housing notch 39 , such that when keypad 80 is compressed against housing 30 by clip 110 a fluid - tight seal is achieved . further , the upward tilt of flange 65 of housing wall 31 at surface 67 allows easier insertion of clip 110 into bore 34 of housing 30 , and also serves to adjust the depth of the clip 110 downwardly within bore portion 60 and accommodate for varying tolerances of the components of control arrangement 20 . according to another assembly method , the clip 110 can be angled downwardly and one edge of clip 110 can be inserted directly into bore portion 60 . the opposite edge of clip 110 is then pushed downwardly past flange 65 and into bore portion 60 . if desirable or necessary , the control arrangement 20 can be removed from the housing wall 31 . specifically , as shown in fig4 , the clip 110 is removed from the housing 30 by inserting a tool behind one or both chamfers 113 of clip 110 and pushing the free ends 112 of clip 110 towards clip recess 114 . this action on clip 110 will cause same to disengage from bore portion 60 , and allow removal of cover plate 100 , keypad 80 and membrane switch 70 . the control or switch arrangement 20 according to the invention as described above self - seals upon assembly of the retainer clip 110 into housing 31 , and thus avoids the need for application of a sealing agent , such as silicone , around or within bore 34 , which is time - consuming and costly from an assembly perspective . additionally , the arrangement according to the invention allows disassembly of the control arrangement for purposes of repair or inspection . it will be appreciated that the scope assembly 11 is shown herein for illustrative purposes only , and various types of surgical tools or instruments other than such scope assembly may incorporate the tool housing structure and control arrangement according to the invention . some of these types of medical instruments are described above , such as surgical saws , shavers and rf probes . other types of medical and surgical instruments may utilize the structure of the invention , and thus this invention is not to be construed as limited for use solely in a scope assembly or in the other surgical instruments described herein . although a particular preferred embodiment of the invention is disclosed in detail for illustrative purposes , it will be recognized that variations or modifications of the disclosed apparatus , including the rearrangements of parts , lie within the scope of the present invention .