an injection molding apparatus according to the present invention is shown generally in the figures at m . apparatus m comprises a nozzle mold plate 20 and a cavity plate 13 cooperating with a mold core 10 along a parting line pl to form a mold cavity 11 therebetween . an injection molding machine ( not shown ) has an injection nozzle ( not shown ) which communicates with a heated runner system 30 via a sprue bushing 32 to provide molten plastic therethrough , under pressure . a locating ring 21 is provided to position the molding machine . runner system 30 communicates through an inlet sleeve or body 17 with an annular melt channel 12 centrally located in an injection nozzle 7 . injection nozzle 7 has a nozzle head 15 and is positioned in a nozzle plate 6 positioned substantially in cavity plate 13 . runner system 30 is maintained at a desired operating temperature by inlet body heater elements 16 , nozzle heater elements 14 and a thermocouple 9 communicating with a suitable control system ( not shown ), as is well known in the art . centrally disposed in melt channel 12 of nozzle 7 is a valve pin 1 which is axially movable in nozzle 7 , for reasons described in more detail below , by the cooperation of an activating cylinder 19 ( which may be pneumatic or hydraulic , as is well known in the art ), and a rack and pinion motion transfer gear train 18 . referring to fig2 valve pin 1 has a stem 1 ′, a neck 4 , a plate or head 2 and a guiding lug or spigot 3 . a removable nozzle tip 8 and a nozzle plate 6 cooperate with neck 4 and head 2 to selectively connect melt channel 12 with mold cavity 11 depending on the position of valve pin 1 , as will be described in more detail below . a spigot notch or bore 5 is provided in core 10 for receiving and guiding valve spigot 3 . spigot bore 5 has a shoulder 34 for receiving valve head 2 , and a core sleeve space 23 is present between shoulder 34 and head 2 when valve pin 1 is in any position other than the “ open ” position , as will be described below . a core sleeve 22 surrounds core sleeve space 23 to prevent melt from penetrating therein . nozzle tip 8 has an enlarged opening 36 in the mold end thereof which cooperates with valve pin 1 to create a nozzle tip gate 24 therebetween . melt channel 12 communicates with opening 36 via a substantially smooth transition zone 38 . valve pin 1 , valve stem 1 ′, valve head 2 , melt channel 12 , transition 38 and opening 36 are substantially circular in cross - section so as to give melt channel 12 an annular shape ( between valve pin 1 and nozzle 7 ) and give gate 24 an annular entry into mold cavity 11 . valve stem 1 ′ has an outside diameter d 1 and head 2 has an outside diameter d 2 , while melt channel 12 has a diameter of m 1 and opening 36 has an inside diameter m 2 . as can be seen from fig2 head 2 diameter d 2 is slightly less than opening 36 diameter m 2 to permit head 2 to be inserted into opening 36 to close gate 24 , as will be described in more detail below . when in the “ closed ” position , as shown in fig2 head 2 is positioned so as to substantially contact tip 8 at opening 36 to close gate 24 . pressurized melt in runner system 30 is thus prevented from entering mold cavity 11 . in this position , core sleeve space 23 has a height of δ 2 , as shown , and part of the outer annular surface of head 2 forms part of the core surface that will shape the hole in the molded part . referring again to fig1 as will be understood by one skilled in the art , cylinder 19 may be selectively actuated and controlled by an appropriate system ( not shown ) to activate rack and pinion gear 18 to effect an axial movement of valve pin 1 within nozzle 7 . from the “ closed ” position ( fig2 ), cylinder 19 , when driven , advances valve pin 1 axially in nozzle 7 through an intermediate position ( fig3 ) to a fully “ open ” position ( fig4 ). referring to fig4 when valve pin 1 is in the “ open ” position , valve pin 1 has moved axially away from nozzle tip 8 , so that gate 24 is opened between head 2 and opening 36 . gate 24 thus provides a passage for heated melt to pass from melt channel 12 in nozzle 7 and into cavity 11 , in response to pressure from the injection molding machine ( not shown ). in the intermediate position ( fig3 ), core sleeve space 23 has a height of δ 1 , but in the fully “ open ” position , there is essentially no core sleeve space at 23 ′ ( see fig4 ). referring to fig1 and 4 , it will be apparent that runner system 30 is annular , unobstructed and continuous throughout melt channel 12 , gate 24 and ultimately mold cavity 11 . the melt flow path around and along valve pin 1 is unrestricted substantially up to the gate 24 , i . e ., the cross - sectional area of this portion of the melt flow path does not appreciably diminish substantially up to the gate . thus there is a simple flow path through which melt may freely flow when the gate 24 is open . this free - flow is advantageous because it assists in reducing pressure losses in the system and permits resin colour changes to be achieved more quickly in the apparatus . the enlarged opening 36 and the cooperation of transition zone 38 and valve neck 4 advantageously permit a larger aperture ring gate 24 to be achieved than is possible with the prior art and without the need for the spreading or distribution means of the prior art , such as those shown variously in u . s . pat . nos . 4 , 340 , 353 to mayer , 5 , 324 , 190 to frei , 5 , 460 , 763 to asai , 4 , 394 , 117 to taylor , no . 5 , 784 , 234 to teng and 5 , 840 , 231 to teng , each of which is incorporated herein by reference . none of these references teaches the use of a transition 38 and enlarged opening 36 to permit a relatively small diameter melt channel 12 to provide melt to a larger aperture part p , as is shown in fig5 while permitting the melt to flow freely , in an unrestricted manner , into the cavity , thereby permitting improved part quality . diameter m 2 of opening 36 is chosen according to the particular application , as will be understood by one skilled in the art , and will be larger than diameter m 1 of melt bore 12 in order to achieve the benefit of an ability to mold larger aperture parts according to the present invention . as shown in the figures , a diameter m 2 that is much larger than m 1 is preferred , and a diameter m 2 of roughly the diameter of tip 8 , or greater , is yet more preferable . one skilled in the art will understand that other modifications are possible . for example , the use of a guide spigot 3 is desirable but not necessary . further , the actuation of valve pin 1 and its movement from the “ open ” to “ closed ” positions may be achieved by other known means . see , e . g ., u . s . pat . no . 4 , 053 , 271 to gellert ; u . s . pat . no . 5 , 916 , 605 to swenson ; u . s . pat . no . 5 , 948 , 450 to swenson ; u . s . pat . no . 5 , 948 , 661 to vorkoper ; u . s . pat . no . 6 , 159 , 000 to puri ; and u . s . pat . no . 6 , 086 , 357 to steil , all of which are incorporated herein by reference . one skilled in the art will understand that the present invention may be applied to single - or multi - cavity injection molds . for multi - cavity applications , melt typically flows through one or more melt distribution manifolds and is injected into each cavity through a respective nozzle , the valve pins of the nozzles being actuated simultaneously , as is well - known in the art . see , e . g ., the camming mechanisms disclosed in u . s . pat . no . 4 , 212 , 627 to gellert , and u . s . pat . no . 6 , 113 , 381 to gellert , both of which are incorporated herein by reference . for example , fig6 shows the multi - cavity arrangement with common valve pin actuating mechanism of the latter patent in which nozzles according to the invention can be used . in this arrangement multiple nozzles 40 are seated in a retainer plate 42 and have commonly actuated valve pins 44 . a melt distribution manifold 46 feeds melt to the nozzles via melt passages 48 . fluid actuators that act directly on the valve pins can be used in a multi - cavity arrangement , and these can be driven simultaneously or separately . u . s . pat . no . 5 , 443 , 381 to gellert ( incorporated herein by reference ) discloses such an arrangement . fig7 shows the fluid drive disclosed in this patent , which can be used in conjunction with nozzles according to the invention . here each nozzle 50 is seated in a plate 52 and has a valve pin 54 actuated by a fluid - driven piston 56 that reciprocates within a cylinder 58 . the piston and cylinder drive 56 , 58 are coaxial with the valve pin 54 . melt is fed to each nozzle laterally from a melt distribution manifold 60 via melt passages 62 . as noted above in connection with the embodiment of fig1 - 4 , valve head 2 , surrounding opening 36 and core sleeve 22 have circular cross - sections and form a ring - shaped gate 24 , resulting in a molded part that has a circular hole as shown in fig8 . it is to be understood that apparatus according to the invention can be used to make parts having large holes of any other regular shape , e . g ., oval ( fig9 ), square ( fig1 ), rectangular ( fig1 ), etc ., or holes of any irregular shape ( see , e . g ., fig1 ), by using mating parts of selected shape . thus , as used in the claims , the term “ annular ” as applied to the gate and the mating parts that define the gate are not limited to circular shapes , and can encompass virtually any closed shape . while the above description includes the preferred embodiment , it will be appreciated that the present invention is susceptible to further modification and change without parting from the fair meaning of the proper scope of the accompanying claims . canadian priority application no . 2 , 317 , 779 , filed sep . 6 , 2000 , is incorporated herein by reference in its entirety .