fig1 is an isometric view of the coin mechanism of the invention , generally 10 , prior to the insertion of coins therein . as shown , the coin mechanism comprises a housing 14 from which a coin receiver cylinder 12 partially extends . the coin receiver cylinder 12 is designed for insertion along its longitudinal axis into the housing 14 after the proper coins have been inserted into the coin slots 22 . a product transport coil 16 with a package of vended product 18 resting therein is shown attached to a coupler member 54 which is connected to the coin receiver cylinder 12 , as will hereinafter be described . to operate the coin mechanism , the proper coins are inserted into the coin slots 22 , after which the coin receiver cylinder 12 is pushed into the housing 14 and rotated to release product . fig1 a is an isometric view of the coin mechanism of the invention following the insertion of the coins showing operation of the mechanism . after the coin receiver cylinder 12 has been inserted into the housing 14 with the proper coins , the receiver can be turned clockwise as shown by the associated arrow . turning of the coin receiver , causes rotation of the coupler member 54 to which the product transport coil 16 is attached . rotation of the coil in the direction of the associated arrow causes advancement of the vended product 18 to a point on the coil where the product at 18 is free to fall therefrom into a chute , not shown , which is accessible to the purchaser . at the same time , the purchase coins 20 fall from the housing 14 to a secure location within the vending machine . one of the notable advantages of the coin mechanism described is that the blocking pawls within the housing which prevent rotation of the coin receiver in the absence of the correct number of coins being located therein , are inaccessible prior to insertion of the receiver , and are therefore protected from tampering . when the coin receiver 12 has been inserted into the housing 14 , the pawls are likewise inaccessible , again protecting the pawls from tampering . it is only when the coin receiver cylinder 12 has been completely inserted inside the housing 14 that there can be any communication of the coin slots with the blocking pawls , and in that condition , the only access to the pawls is by the coins in the slots ; consequently , only they are able to force the pawls into a non - blocking position . fig2 is a top plan view of a coin receiver cylinder of the invention , generally 12 . the figure includes an operating handle 24 attached to a security flange 39 . a guide tab groove 35 is located between the security flange 39 and the body of the coin receiver 13 . the guide tab groove 35 is adapted to receive guide tabs 27 , better seen in fig5 after the coin receiver has been fully inserted into the coin mechanism housing . receiver guide slots 26 , 26a , and a portion of slot 31 are adapted to form a track for guide tabs 27 as the coin receiver 12 is inserted into the housing of the coin mechanism . shown in the figure are coin slot partitions 25 , which include a coin - lifting notch 23 , whose purpose is described in more detail in connection with fig2 a . also illustrated in fig2 is a guide block receiver 30 whose function is to receive and guide the guide block 58 of the coupler member 54 , shown in fig4 . further seen in the figure are shoulder stops 28 and 29 which constitute the dual , independent blocking means of the mechanism which engage the blocking pawls when the correct coins have not been inserted into coin receiving slots 22 . an access port 46 is located in the coin receiver which enables travel of the receiver into the housing 14 to be controlled by travel limit pin 68 , shown in fig5 . a notable advantage of the coin mechanism of the invention resides in its relatively small height and width , which allows multiple mechanisms to be installed side - by - side in more limited space in a vending machine than would otherwise be possible . within such considerations , the dimensions of the coin receiver cylinder 12 can be varied relatively broadly ; however , typically the receiver will be about 11 / 2 inches in diameter and about 13 / 4 inches to 2 inches long . in such case , the guide blocl receiver will be about 1 inch deep and approximately 3 / 8 × 3 / 8 inch square . fig2 a is a cross - sectional view of a coin receiver cylinder of the invention along line 2a -- 2a of fig2 . receiver guide slots 26 and 26a are shown located in the cylinder body 13 , as is slot 31 with its associated shoulder pawl stop 28 located on one end thereof . coin slot partition 25 is also illustrated , showing shoulder pawl stop 29 and coin - lifting notch 23 located therein . also shown is an end view of guide block receiver 30 , the dimensions of which have previously been described . the guide slots not only facilitate back and forth movement of the coin receiver 12 within housing 14 , but serve to prevent deliberate misalignment or &# 34 ; cocking &# 34 ; of the cylinder in the housing in efforts to fraudulently manipulate the blocking pawls to unblock the coin mechanism and thereby obtain product without payment therefore . the coin slots themselves are about 1 inch wide and about 7 / 8 inch deep , each having a width of about 1 / 16 inch . fig3 is a front view of a housing of a coin mechanism of the invention , generally 14 . shown is a receiver passageway 15 , adapted to receive the body 13 of coin receiver 12 . the passageway is provided with a guide pin slot 44 which receives guide pin 74 , seen in fig5 b , and which controls the extent to which the coin receiver 12 can be withdrawn from the front of housing 14 . access port 46 communicates with guide pin slot 44 allowing the longitudinal travel of the coin receiver 12 to be further limited by insertion of travel limit pin 68 . at the far , or rear end of receiver passageway 15 are located two annular grooves , 48 and 50 respectively , concentric to the passageway . groove 50 is designed to receive a ratchet wheel 56 , better seen in fig4 a , while groove 48 provides a race for the travel of guide pin 74 after the coin receiver 12 has been fully inserted into housing 14 and rotated . ratchet pawl 52 prevents the ratchet wheel 56 from being rotated in a direction opposite to the proper operating direction of the coin receiver 12 . a blocking pawl , generally 32 , is mounted on pawl mounting pin 34 , consisting of a bifurcated structure comprising a pawl spring arm 33 , which serves to force blocking pawl tip 40 at the end of pawl arm 43 into the receiver passageway 15 . a pawl cam surface 38 is located between the pawl mounting pin 34 and the pawl tip 40 . a pawl deactivation pin 36 is also shown whose purpose is described in connection with fig3 c . like the coin receiver 12 , the dimensions of the housing 14 can be varied rather widely . in the case of a coin receiver having dimensions as described in the preceding , the housing will commonly be approximately 21 / 4 inches wide by 21 / 2 inches high . such a housing will be about 2 inches deep . importantly , the housing 14 is provided with a housing recess 37 , and in the case of a housing having the dimensions outlined , the recess will be about 3 / 4 inches deep . fig3 a is a side elevation of the housing of fig3 through which receiver passageway 15 extends , communicating with the annular grooves concentric therewith , 48 and 50 respectively , the function of which has been described in the preceding . also shown is ratchet pawl 52 whose purpose has likewise been indicated . pawls 32 , mounted on pin 34 , and which include pawl cam surface 38 and pawl tip 40 , are shown in a position in which two of the pawls are deactivated by deactivation pin 36 , all of the pawls being located in housing recess 37 . coin chute 42 through which the coins are discharged from the coin mechanism 10 into a secure area is also illustrated , and the positioning of access port 46 can be clearly seen . as will be appreciated , the travel of the coin receiver cylinder 12 is determined by the distance which guide pin 74 is able to travel along slot 44 until it reaches the end of the slot , but it can also be limited by insertion of travel limit pin 68 in access port 46 . by suitably curtailing the travel of the coin receiver 12 , fewer of the coin slots 22 are exposed , providing one method for determining the coins that can be inserted in the receiver , and therefore of controlling the price of the goods vended . fig3 b is a rear elevation of the housing of fig3 . the figure shows the housing 14 through which the receiver passageway 15 extends , communicating with the annular grooves 48 and 50 , concentric to passageway 15 . the housing has a recess 37 therein , in which the pawls 32 are disposed , the pawl tips 40 of which in their blocking mode are urged inwardly toward the center of the passageway 15 . the coin receiver cylinder travel - limiting guide pin slot 44 is shown , as is access port 46 which as indicated , can be used to further limit the travel of the coin receiver 12 . also shown is ratchet pawl 52 partially blocking groove 50 to prevent improper rotation of the coin receiver as previously explained . fig3 c is a partial front view of a housing of the coin mechanism of the invention showing blocking pawls of the mechanism in an immobilized position . the figure shows a housing 14 in which some of the pawls 32 have been forced outwardly , away from passageway 15 , so as to be incapable of engaging blocking shoulder stops 28 and 29 . the pawls are held in an immobilized position within housing recess 37 by means of pawl deactivation pin 36 , also seen in fig3 a . the dimensions of the pawls will depend upon the other dimensions of the coin receiver 12 and the housing 14 ; however , in the case of the dimensions already outlined , pawl arm 43 will be about 2 inches long , while the pawl spring arm 33 will be about 1 inch long . typically , approximately 1 / 8 inch will be provided between the bifurcated arms to accommodate the distance that the arms can be moved toward each other to provide the necessary elasticity of one relative to the other . the thickness of pawls in such case will be about 3 / 8 inch . fig4 is a side elevation of a coupler of the invention , generally 54 . the coupler member comprises a ratchet wheel 56 attached on one side to a transport coil connector cylinder 61 , and on the other to a guide block 58 which contains a spring receiver chamber 60 . the spring receiver chamber is designed to accommodate spring 66 , better seen in fig5 which serves the purpose of urging the coin receiver cylinder 12 away from the housing 14 so that coins can be inserted therein . the transport coil connector cylinder 61 has a transport coil connector slot 62 located therein to permit attachment of the product transport coil by means well known in the art . the ratchet wheel 56 by its interaction with ratchet pawl 52 serves to prevent improper rotation of the coin receiver 12 . by preventing improper rotation , the ratchet wheel 56 prevents damage to the mechanism , and also prevents continued manipulation in an attempt to defeat the mechanism . fig4 a is a front elevation of the coupler member of fig4 generally 54 . the figure shows the ratchet wheel 56 and the transport coil connector cylinder 61 . also shown is the connector slot 62 of the connector cylinder 61 , provided for the purpose of attachment of the product transport coil 16 . guide block 58 with its spring receiver 60 can also be seen . the dimensions of the coupler member 54 may be broadly varied , but in conjunction with the components having dimensions previously described the rachet wheel will be about 13 / 4 inches in diameter , while the guide block will be about 1 inch long , about 3 / 8 inches high and 3 / 8 inches wide ; typically , the spring receiver will have a diameter of about 1 / 4 inch . fig5 a and 5b show an exploded view of the coin mechanism of the invention . assembly involves insertion of coin receiver cylinder 12 through guide plate 70 into passageway 15 of housing 14 . guide tabs 27 serve to locate and stabilize the coin receiver cylinder 12 , being received , for example in receiver guide slot 26 . pawls 32 are mounted within housing recess 37 on pawl mounting pin 34 , pawl deactivation pin 36 being provided optionally to deactivate one or more of the pawls , as previously described . guide pin 74 urged outwardly by spring 72 both guides and limits the longitudinal movement of the coin receiver cylinder 12 as it moves in and out of the passageway 15 . the movement of the coin receiver cylinder 12 is further limited by the optional insertion of travel limit pin 68 . a coupler member 54 serves to connect the product transport coil 16 to the coin receiver cylinder 12 . such connection is effected by the insertion of guide block 58 into guide block receiver 30 , and a spring 66 is provided between the two elements to cause the coin receiver cylinder 12 to be urged outwardly from the front of housing 14 . a ratchet wheel 56 is received into annular groove 50 , and with its cooperation with ratchet pawl 52 prevents rotation of the coin receiver cylinder 12 in a non - operating direction . connection between the product transport coil 16 and the coupler member 54 is made possible by connection of the coil to connector cylinder 61 . coupler member 54 is retained within housing 14 against the urging of spring 66 by means of a retainer clip 64 fastened to housing 14 . although metal can be used , the principal parts of the coin mechanism 10 , including the coin receiver cylinder 12 , housing 14 , coupler member 54 and pawls 32 , are preferably made from plastic since this permits them to be inexpensively fabricated , for example , by injection molding or other techniques well known in the trade . any of a variety of plastics can be employed for the purpose , including particularly those of the thermoplastic type such as , for instance , nylon , abs , acrylics , polycarbonates , acetals , polystyrene , and others . fig6 is a semi - schematic drawing of the coin mechanism of the invention showing an interior view of the mechanism in a first blocking position . as shown , the coin receiver 12 is inserted in passageway 15 . in the figure , no coin has been inserted in the coin slots of the coin receiver cylinder ; however , an attempt has been made to rotate the cylinder in its clockwise , operational direction . as a consequence , the pawl tip 40 of pawl 32 has engaged the blocking shoulder stop 28 forming one end of slot 31 , preventing further rotation of the coin receiver 12 . the pawl 32 , mounted on pawl mounting pin 34 is forced into its blocking position by the pawl spring arm 33 . as can be seen , in its blocking position pawl tip 40 is forced against the edge 45 of housing recess 37 by the abortive attempt to rotate the coin receiver 12 , resulting in pawl tip 40 being placed in compression during the blocking process . the pawl tip is well adapted to withstand compression stressing ; consequently it is not only able to withstand attempts to force the cylinder and to defeat the mechanism , but because the pawls are only subjected to compression stressing they are characterized by long life . fig6 a is a semi - schematic drawing of the coin mechanism of the invention showing unblocking of the blocked mechanism illustrated in fig6 . in the figure , a coin 20 has been inserted in a coin slot of the mechanism , adjacent the pawl 32 . during rotation of the coin receiver cylinder 12 in passageway 15 , the camming surface 38 of the pawl is forced away from the passageway 15 , against the force of the pawl spring arm 33 , displacing pawl tip 40 away from shoulder stop 28 , allowing rotation of the receiver cylinder to continue . fig7 is a semi - schematic drawing of the coin mechanism of the invention showing an interior view of the mechanism in a second blocking position . the figure shows a situation in which the coin mechanism 10 has been forced , or has malfunctioned , allowing the coin receiver 12 to proceed beyond shoulder stop 28 . in such case , urged by pawl spring arm 33 , the pawl tip 40 of pawl 32 has engaged shoulder stop 29 , preventing further rotation of the coin receiver cylinder 12 in passage 15 . fig7 a is a semi - schematic drawing of the coin mechanism of the invention showing the unblocking of the blocked mechanism illustrated in fig7 . the figure is really a continuation of the condition shown in fig6 a in which the coin receiver cylinder 12 has been rotated in passageway 15 beyond shoulder stop 28 . as a consequence of the presence of coin 20 in the coin receiver cylinder 12 , the pawl tip 40 of pawl 32 has been forced against the urging of pawl spring arm 33 outwardly into housing recess 37 , preventing engagement of the pawl tip with shoulder stop 29 . this allows the coin receiver cylinder 12 to continue its rotation to the point at which the coin 20 falls through opening 42 into a secure area of the coin mechanism . the device of the invention described defeats attempts to steal merchandise from vending machines equipped with the coin mechanism in a number of ways in addition to those described in the preceding , as follows . for example , the coin mechanism of the invention provides a housing recess 37 and clearance space 41 which allows a coin protruding from a coin slot to progress to coin chute 42 without hinderance ; however , if an attempt is made to wedge the coin into the coin slot in order to prevent its falling therefrom so that the coin receiver can be continuously rotated with the same coin , the lack of any clearance between the coin receiver cylinder 12 and the housing 14 at the left side of the mechanism , as seen in the figure , prevents the coin from preceding beyond the coin chute 42 , defeating the attempt . furthermore , if an attempt is made to use a coin of a smaller dimension than the correct coin , for example a penny rather than a quarter , through the artifice of inserting a filler in the bottom of the coin slot to raise the height of the smaller coin to equal that of the larger size coin , then as the coin receiver cylinder is rotated , the coin will roll to the side of the coin slot opposite shoulder stop 29 , resulting in engagement of pawl tip 40 with shoulder stop 29 , again preventing defeat in the machine . from the foregoing , it will be seen that the pawls of the mechanism , together with this dual shoulder stops provide double protection for the mechanism , a significant advantage in the event one of the blocking shoulder stops fails for some reason . the dual shoulders also prevent the coin receiver from being accelerated to a velocity at which engagement of the pawl tip 40 with a single shoulder stop could fail to occur . location of a first shoulder stop proximate to the point at which rotation of the coin receiver has just begun , also prevents appreciable rotation of the receiver in the absence of inserted purchase coins . fig8 is an isometric view of a coin alteration plug of the invention . a method by which the number of coins required to operate the coin mechanism of the invention can be changed has already been described , i . e ., by inactivation of one or more of the pawls with a pawl deactivation pin 36 , with or without a reduction in permissible travel of the coin receiver by appropriate location of travel limit pin 68 . from time - to - time , however , it also becomes desirable to change the value , and therefore the dimensions of the coins required to operate the mechanism . in such instances , the use of a coin alteration plug 76 is desirable . such a plug comprises an insert having an opening 82 dimensioned to receive a different sized coin . the insert is provided with locking tabs 78 which can be temporarily bent as a consequence of the provision of tab bending notches 77 and inserted in tab notches 80 , better seen in fig8 a . fig8 a is a front elevation of a coin alteration plug of the invention , inserted in a coin slot of a coin receiver cylinder 12 . as shown , a coin alteration plug 76 has been inserted in a coin slot , each end of the bottom of which has an undercut notch 80 . insertion is accomplished by compressing the locking tabs 78 in the direction of the tab bending notches 77 , allowing the plug to be inserted adjacent to the coin slot partition 25 . once the bottom of the plug reaches the bottom of the coin slot , the elasticity of the locking tabs propels them outwardly into the tab notches 80 , locking the plug securely in position . while in accordance with the patent statutes , a preferred embodiment and best mode has been presented , the scope of the invention is not limited thereto , but rather is measured by the scope of the attached claims .