Abstract:
An ergonomic, self contained hand-held thread inspection tool is power driven, which uses a mechanical clutch as a surrogate for torque to initiate automatic reversal and gauge withdrawal in case of jamming. The distal end carries the thread gauge attached to a motor-driven spindle. A thread depth collar sleeve, adjustable by manual turning, concentrically surrounds the thread gauge. When threaded into a blind hole or onto a protruding stud and operated, the distal end of the thread depth collar sleeve comes in contact with a part, pushing it against spring force. This movement is internally sensed, causing an indicator to flash, signaling “test OK”, while automatically reversing the spindle to withdraw the thread gauge. If during the forward excursion of the thread gauge a torque exceeding the pre-set torque limit is encountered, a buzzer is sounded signaling an over-torque problem and the spindle is simultaneously reversed for automatic gauge withdrawal.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of application Ser. No. 12/220,284 filed Jul. 23, 2008 and claims priority in part pursuant to 35 U.S.C. §120 therefrom. That application is incorporated by reference herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to portable thread inspection tools. 
       BACKGROUND OF THE INVENTION 
       [0003]    Thread inspection is a necessary part of many manufacturing or quality control procedures. It involves the spinning of externally or internally threaded gauges into threaded holes or onto threaded studs respectively. These threaded holes or studs may be integral parts of machines or perhaps just fastener parts such as nuts or bolts. Power driven spindles on which gauges are fitted to facilitate rapid and uniform testing are used. 
         [0004]    The prior art includes U.S. Pat. No. 4,926,700 of Peplinski for a blind hole thread gauge using a modified commercial nut driver. This bench mounted device uses strain gauges to monitor torque during testing, as well as sensing when a given hole has been tested to its proper depth. U.S. Pat. No. 7,059,055 of Wickham et al. is a commercial tester for checking thread presence in blind holes rapidly. Both single spindle and multi-spindle devices are described using adjustable slip clutches to limit the torque applied during testing. Upon detecting the proper depth of testing or upon exceeding the torque limit, the tester automatically reverses the drive motor to disengage the gauge from the hole being tested. 
         [0005]    Additionally, Peplinski &#39;700 uses an electrical contact at the distal end, which closes a circuit when it touches the machine part. This electrical contact is rotated with the gauge, causing possible abrasion at the point of moving contact. 
         [0006]    The prior art does not reveal a compact hand-held ergonomic thread inspection tool that is power driven, and uses a mechanical clutch as a surrogate for torque to initiate either automatic withdrawal or alert the user to operate the reversing switch manually in case of jamming. 
         [0007]    The prior art also shows the compact hand-held manual adjustable torque thread gauge of Kolkind (U.S. Pat. No. 7,484,427). This interposes an adjustable magnetic torque limiting clutch between the handle, which is manually rotated, and the thread gauge at its front end. 
       OBJECTS OF THE INVENTION 
       [0008]    It is an object of the present invention to provide a compact hand-held ergonomic thread inspection tool that is power driven, which uses current draw or a mechanical clutch as a surrogate for torque to initiate automatic reversal and gauge withdrawal in case of jamming. 
         [0009]    Other objects which become apparent from the following description of the present invention. 
       SUMMARY OF THE INVENTION 
       [0010]    In keeping with these objects and others which may become apparent, the present invention is a thread inspection tool which is configured as a hand-held cylindrical housing that is self-contained, including a compartment for rechargeable batteries to power the motor-driven spindle. An optional AC sourced power supply and battery charger can alternatively supply the low voltage DC power to run the thread checker via DC power cord and also simultaneously charge the batteries (if installed). 
         [0011]    A transparent panel on the inspection tool protects adjustment switches from inadvertent operation while permitting a view of a small display showing the current torque limit setting. It can be opened to provide access to the torque adjusting switches and the metric/English units switch. Once the desired torque limit is set, any number of threaded holes, blind threaded holes, or threaded studs or bolts can be checked using the same setting. 
         [0012]    The distal end carries the thread gauge attached to a motor-driven spindle. As an ergonomic feature, a thread depth collar sleeve, simply adjustable by manual turning, concentrically surrounds the thread gauge. When threaded into a blind hole or onto a protruding stud and operated, the distal end of the thread depth collar sleeve comes in contact with machine part pushing it in slightly against light spring force. This movement of less than a pre-determined threshold, such as, for example, 1/32″ or otherwise, is internally sensed, causing an indicator to flash, signaling “test OK”, while automatically and simultaneously reversing the spindle to withdraw the thread gauge. If during the forward excursion of the thread gauge a torque exceeding the pre-set torque limit is encountered, a buzzer is sounded signaling an over-torque problem (such as a thread jam); the spindle is simultaneously reversed by either automatic gauge withdrawal or by using the reversing switch manually. Note that when a spindle is automatically reversed either due to a thread depth limit or an over-torque indication, this reverse spindle powering is performed with full torque available since the torque limit sensing is defeated during this reverse excursion. 
         [0013]    Since both right-hand as well as left-hand threads require inspection, the operating switch for starting the spindle turning is direction sensitive. It is, for example of one type of switch, a momentary type rocker switch, which responds to pressing the forward end by turning the spindle clockwise while pressing the rearward end causes counterclockwise rotation. Other types of switches may be used, such as toggle, slide or membrane switches. The orientation of the switch can be either front to back or side to side switch A momentary switch is used to require the operator to continually press on the switch to keep the spindle moving (even through automatic reversal) as a safety feature. The spindle will stop when pressure is removed from the rocker switch. The switch can also be used for manual reversal of the spindle motor at any time. 
         [0014]    A DC permanent magnet gearmotor is used to turn the spindle at a slow speed, such as, for example, 150 to 200 rpm, or other desired slow speeds. This type of motor has a torque constant expressed simply in terms of oz-in/amp or N-m/amp at the motor shaft. The torque at the output of the gear box (which spins the gauge spindle) can be deduced from current draw of the motor by simply reading the current, applying the torque constant, and then multiplying by the reciprocal of the gearbox speed reduction ratio (GBR). This works well when the torque to be detected is large as compared to the parasitic no-load and running torque introduced by internal gearbox friction and lubrication viscous losses. In fact, the GBR and the motor torque constant remain stable over the life of inspection tool, and they are factors well known at gearmotor manufacture. Another constant defined here is the motor torque factor (MTF) which is the reciprocal of the motor torque constant. In addition, other relevant gear box and motor parameters are defined. By testing a number of manufactured gearmotors in a laboratory setting and averaging the results, an estimate of the gear box friction factor (GBF) as well as an additive current factor representing no-load torque (AF) can be obtained. In the preferred embodiment, the desired torque limit is combined with the other factors mentioned to better approximate the detected motor current truly representative of the desired torque limit. These constant parameters are combined in an algorithm with the desired torque to arrive at the current estimate as follows: 
         [0000]      limit current=(GBR×GBF×MTF×Desired torque)+AF 
         [0000]    Then the motor current is continuously measured and compared with this limit current value to determine if the desired torque limit at the thread gauge is exceeded. 
         [0015]    In an alternate embodiment with extended low-end thread inspection range, the effects of the gear box are more precisely estimated in the field by establishing a built-in calibration subsystem and procedure. The GBF and AF factors are determined by the calibration procedure and then updated in the limit current algorithm used during actual inspection testing. By pressing a calibrate button and running the spindle with no load in the desired direction, the actual AF current value is measured. Since AF is correlated with GBF as per actual empirical trials by sampling and testing a number of sample units, a better estimate of GBF is obtained from an empirical table stored at the thread inspection tool as retrieved using the measured AF as an index into the table. One variable that affects gear box factors is temperature, another is gear tooth wear. Both of these variables are compensated by a periodic field calibration procedure. 
         [0016]    As an alternative to using an algorithm to account for factors, a simple table look-up procedure using desired torque limit as an index to find estimated current can be used. If a calibration procedure is used with such a system, the calibration would enter different updated table entries derived from factory testing. These values are retrieved as a vector using the measured AF as an index. 
         [0017]    Although space for electronic controls is limited within the inspection tool of this invention, the use of a single chip appliance grade microcomputer can substitute for discrete logic components and other peripheral chips saving board space as well as cost. In addition, the use of a flexible polyimide board substrate can extend available board area by using the curved area adjacent to the inner housing wall. 
         [0018]    In summary, a handheld or a table countertop mounted precision thread inspection tool includes a portable, compact held elongated housing having a distal end and a proximate end. A thread gauge protrudes from the distal end of the housing. A means is provided for setting a length of the thread gauge extending from the distal end of the housing. A drive for the thread gauge includes an electric motor in the housing and a coupling between the motor and the thread gauge. 
         [0019]    Torque produced by the electric motor as the gauge is driven into a blind hole or onto a stud is monitored. when a predetermined limit of torque is exceeded, an alarm is set off and automatically the direction of rotation of the thread gauge is reversed. 
         [0020]    Preferably, the torque is monitored by monitoring current draw of the motor, which may be, for example, a DC permanent magnet gearmotor. The current draw limit is related to the predetermined torque limit by incorporating empirically determined gear box parameters, such as gear box ratio (GBR), gear box friction factor (GBF), and an additive factor (AF) in addition to the motor torque constant. 
         [0021]    Optionally, the housing of the thread inspection tool includes a collar threaded into the distal end of the housing, wherein the thread gauge is mounted within the collar and is fixed along a longitudinal axis of the housing, whereby the length of thread gauge protruding out of the housing is set by manual rotation of the collar. 
         [0022]    The housing of the thread inspection tool preferably has a mid-section with a transparent cover containing a display and switches for setting the predetermined limit of torque for forward spinning of the thread gauge. 
         [0023]    The collar of the thread inspection tool is preferably part of a sub-system mounted in the distal end of the housing, such that the sub-system is movable along the longitudinal axis of the housing and biased in a forward direction, toward the distal end of the housing. The housing has a sensor, such as, for example, a snap action switch, an optical sensor or a Hall effect switch, which detects when the sub-system overcomes the bias and is moved rearwardly a predetermined distance indicating that the thread gauge no longer has forward movement, because the thread gauge has moved fully into the blind hole or onto the stud. Moreover, the housing has an indicator light which flashes when a thread test is successful. The spindle is simultaneously reversed by either automatic gauge withdrawal or by using the reversing switch manually. 
         [0024]    The housing preferably has a momentary rocker switch for controlling operation of the motor, and preferably includes a battery as a power source for the motor, with a socket for recharging the battery or for operating the motor. Other types of switches may be used, such as toggle, slide or membrane switches. The switch can be either a front to back switch or side to side switch. 
         [0025]    The coupling between the motor and thread gauge preferably includes a spindle having a coupling. The thread gauge includes a thread portion and a coupling portion, wherein the coupling portion of the thread gauge engages with the spindle coupling in such a manner that the thread gauge is readily replaceable with a different thread gauge. 
         [0026]    An optional field calibration procedure including pressing the rocker switch in a predetermined direction while a calibrate switch is on. This procedure obtains an actual no-load current reading at any desired time, whereafter the no-load current reading is then converted to a digital value representing a factor AF in an algorithm associated with each current reading. The field calibration procedure also uses the no-load current reading to retrieve an accurate the gear box friction factor (GBF) for the algorithm from a stored table of empirical values. 
         [0027]    An optional table mount accessory for convenient bench-top use of the hand-held thread inspection tool of this invention is also described. It includes a base with a split round clamp attached which receives the housing of the thread inspection tool and locks it in place via a tightening screw with a knob. An adjustable rest in registration with the front end of the thread inspection tool can then be used to support the threaded unit under test. 
         [0028]    In an alternate embodiment, the ergonomic depth adjusting subsystem of the previous embodiment is incorporated into a compact thread inspection tool which uses an adjustable mechanical clutch to limit the torque applied to the thread gauge, instead of using the monitoring of motor current to implement that feature as discussed in the first embodiment. 
         [0029]    In this mechanical clutch embodiment, the housing also includes a collar threaded into the distal end of the housing. The thread gauge is mounted within the collar and fixed along a longitudinal axis of the housing, whereby the length of the thread gauge protruding out of the housing is set by manual rotation of the collar. 
         [0030]    The sequence of operation for the version with a mechanical clutch starts with pressing a membrane or other switch for a desired rotation. The operator continues pressing the membrane or other switch during the inspection cycle. If the mechanical clutch slips, torque is exceeded and the user depresses the return on switch, thereby reversing the motor manually. 
         [0031]    Alternatively, when the part being inspected reaches the adjustable depth reversing stop, the adjustable depth reversing stop, locking nut and depth control sleeve engages the reversing switch, which activates a reversal of rotation of the thread gauge, illuminating the reverse rotation indicating light. Alternatively, when inspection of the part being inspected is complete, removing pressure on the membrane switch or other switch will automatically reset the tool. Optionally an alarm may be set off and reversal of direction of the thread gauge occurs when a length setting limit is reached. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]    The present invention can best be understood in connection with the accompanying drawings. It is noted that the invention is not limited to the precise embodiments shown in drawings, in which: 
           [0033]      FIG. 1  is a perspective view of the thread inspection tool of this invention; also shown is optional AC sourced DC power supply and charger; 
           [0034]      FIG. 2  is a side exploded view of the depth adjusting subsystem; 
           [0035]      FIG. 3  is a side crossectional view showing the mechanical components; 
           [0036]      FIG. 4  is a high level operational flow chart of the thread inspection tool; 
           [0037]      FIG. 5  is a logic flow diagram showing hardware features which can also be implemented in software using a microcomputer; 
           [0038]      FIG. 6  is a crossectional view of the area layout for electronics using flexible polyimide board extensions; 
           [0039]      FIG. 7  is a high level flow chart of a field calibration procedure; 
           [0040]      FIG. 8  is a side elevation of the table mount accessory showing the position of the thread inspection tool within the mount in dashed lines; 
           [0041]      FIG. 9  is a top view of the table mount of  FIG. 8 ; 
           [0042]      FIG. 10  is a back end view of the table mount accessory with no inspection tool in place. 
           [0043]      FIG. 11  is a perspective view with a partial front end cut-away of an alternate mechanical clutch embodiment of the thread gauge of this invention; 
           [0044]      FIG. 12  is a perspective cut-away showing the internal components of the thread gauge with a mechanical clutch shown in  FIG. 11 ; and, 
           [0045]      FIG. 13  is a flow chart describing the operation of the alternate embodiment thread gauge with a mechanical clutch. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0046]      FIG. 1  shows the thread inspection tool  1  of this invention. Thread gauge  2  is surrounded by depth limit collar  3  shown at a setting of “D”. Item  4  is a lock nut which locks the internal parts of the depth setting subsystem located within front housing section  5  which screws into mid housing  6  which also contains electronics. Transparent cover  14  covers a liquid crystal display as well as switches which set the torque limit for forward spinning of gauge  2 ; it is opened to make torque changes. Momentary rocker switch  12  controls spinning of the gauge spindle while flashing indicator light  10  denotes a successful thread test. Other types of switches may be used, such as toggle, slide or membrane switches. The switch orientation can be either a front to back switch or side to side switch. Housing compartment  7  contains the motor, such as a gearmotor as well as a power source, such as one or more batteries, to power the inspection tool. Cap  8  permits access to batteries within. Optional socket  15  mates with DC power plug  23  on DC line  22 . This supplies low voltage DC, typically 12 volts, from power supply/charger  20  which is optional. Charger  20  can charge batteries in housing  7  using plug-in AC ( 21 ) power, or it can power tool  1  directly even with batteries removed. 
         [0047]      FIGS. 2 and 3  should be viewed together for better understanding.  FIG. 2  shows the depth setting subsystem including several concentric hollow parts. Internal sleeve  25  has a collar  26  at its distal end, internal threads  27  for its entire length, external threads  28  at the front end, and preferably a protruding anti-rotation member, such as key  29 . This fits inside housing section  5  when key  29  is in registration with internal groove  35  of housing  5  and rests with collar  26  against ridge formed by reduced diameter section  34 . Internal threads  32  attach housing  5  to housing  6  section. Depth limit collar  3  has external threads  42  which engage the internal threads  27  of sleeve  25 . Preferably a friction reducer, such as rubber O-ring  45  is a stretch fit onto collar  3  and also fits within region  51  of lock nut  4  with exit hole  52  permitting access for the end of collar  3 . A spring ferrule can be used as a substitute for O-ring  45 , thereby serving the same function. Biasing members, such as, for example, two or more small springs  40 , are partially retained within radially equi-spaced holes  36  in the front end of housing section  5 . They bias the subassembly including of internal sleeve  25 , collar  3 , O-ring  45  and lock nut  4  forward under light spring force relative to housing  5  (after lock nut  4  is tightened). If collar  3  is pressed back relative to housing  5 , it can move a predetermined distance, such as, preferably, about 1/32″ or other suitable distance; this is enough to trip a switch, such as, for example, snap action switch  70  (see  FIG. 3 ). An optical sensor or a Hall-effect sensor can be used as a replacement for switch  70 , but in any event the objective is to sense the movement of collar  26 .  FIG. 3  also shows ring  55  which can be screwed into internal threads  43  of depth limit collar  3  to provide an end surface more closely fitted around the outer diameter of gauge  2 . Note that collar  3  in use is non marring to the surface on which it impinges since it requires little force and it is non-rotating. Note that the use of O-ring  45  provides an optimal amount of friction when manually turning depth limit collar  3 ; it is easy to turn while having enough friction to maintain a setting during use. 
         [0048]    In  FIG. 3 , the end of battery pack  63  is shown in a portion of housing  7  behind gearmotor  62 . The shaft  65  of gearmotor  62  engages coupling  61  which engages spindle shaft  67  carried in retainers, such as two ball bearings  60 , one at each end of housing section  6 . The front end of spindle  67  opens into an integral female taper coupling. Note area  57  is shown empty, this is where the electronic subassembly is preferably housed. An intermediate coupling  68  is preferably used, having a male taper coupling which mates with that integral to spindle shaft  67 . The front female taper of coupling  68  may be different to accommodate whatever male taper is integral to gauge  2 . Intermediate coupling  68  is therefore a conversion coupling. Many different such couplings are provided as needed. Lateral holes to facilitate disengagement rods are shown at the apex of female taper couplings. The entire depth limit subassembly can be unscrewed from housing  6  intact and pulled forward of gauge  2  to facilitate changing gauges and/or conversion couplings. 
         [0049]    The flow chart of  FIG. 4  describes the normal procedure for using the thread inspection tool of this invention. It is presumed that the torque limit for the usage had been previously set. Operation starts by pressing the rocker switch in the desired rotation direction. It remains pressed during the entire procedure. When the motor starts, the gauge is placed in the blind hole or onto the stud to be tested and the rest of the procedure is automatic until the finger is released from the rocker switch. Torque is monitored during the forward motion by monitoring the current draw of the motor. If the limit is exceeded, an alarm signal (such as a buzzer) is sounded and the spindle is automatically reversed so as to turn in a direction opposite to that of the still pressed rocker switch. Alternatively, the switch is used manually for reversal after being alerted by the alarm and stopping automatically (this is shown in dashed lines in  FIG. 4 ). The reverse direction is engaged with no torque limit. If the depth limit is encountered before any torque limit is detected, an indication of “test OK” is given (flashing light) while proceeding to an automatic reversal to withdraw the thread gauge. 
         [0050]      FIG. 5  is a logic diagram showing the preferable details of the tool operation and torque setting as if discrete hardware logic modules were used. A more cost effective and compact implementation would substitute software routines to implement equivalent logic manipulations using a single chip appliance class microcomputer. Rocker switch S 1  (also shown as  12  previously) determines the direction setting of the bridge motor driver (a bulkier relay can also be used) while an exclusive OR detecting either direction engagement of switch S 1  keeps the bridge driver enabled. A flip flop (FF) with set/reset/toggle inputs stores the current direction setting of the motor. The capacitors coupling the inputs insure that only initial pulses are considered. Considering only the depth limit switch S 2  (previously  70 ), motor keeps operating in the same direction until S 2  is closed which causes FF to toggle the direction input of the bridge driver thereby reversing the motor. Separately, a set/reset (SR) latch stores the fact that S 2  had been closed (at least momentarily) and indicates this fact by lighting flashing light “OK” or  10 . In the meantime, torque output is being monitored via the voltage across resistor Rs in series with motor supply lead (12V). This is amplified and compared with a voltage previously set representing the voltage of the desired torque limit. (Note that a Hall effect current measuring device can be used instead of the sense resistor.) If this limit is exceeded prior to switch S 2  having been closed, comparator C sets a set/reset (SR) latch which sets a buzzer as a problem indicator while also keeping toggle input of FF in the low (engaged) position; the latter reverses the spindle motor and prevents further over-torque detections from interfering. Some details such as inhibits and resets have not been discussed. 
         [0051]    The torque setting portion of  FIG. 5  involve the optional use of momentary switch buttons S 3  and S 4  which are protected by cover  14 . These cause a slow counter to cycle up or down displaying the desired torque at the spindle output on a liquid crystal display in either metric (N-M) or English units such as oz-in as set by slide switch S 5 . The count output “torque” is input to an algorithm solver along with known constants for gear box ratio (GBR), gear box friction factor (GBF), motor torque factor MTF, and an additive factor (AF) related to no-load current. The output is a digital value of the motor current related to the desired torque limit. This is then passed through a D/A converter to convert it to a properly scaled analog voltage for comparison in an analog comparator. 
         [0052]      FIG. 6  is a crossectional detail showing an optional electronics board  75  with switches and display facing transparent cover  14  and components on the back side. Board  75  is attached through a hatch in the wall of housing  6 . Flexible polyimide board extensions  76  can provide much more area to accommodate more electronic components thereby using the enclosed area around shaft  67  effectively. 
         [0053]      FIG. 7  is a flow chart showing the procedure for field calibration. This is an alternate embodiment which would be warranted only if a very wide range of desired torque limits are required in the inspection tool. This feature improves the accuracy of torque limit settings especially important for the low end of settings. It can compensate for changes in the gear box including tooth wear and loss of lubricant, or temperature variations. The operation is started by operating the rocker switch in the desired direction while the calibrate switch is on. The idea is to obtain an actual no-load current reading which can be obtained from point CS in  FIG. 5 . This is then converted to a digital value and becomes factor AF in the algorithm. A table of empirical values of factor GBF related to different values of AF is stored within each thread inspection tool. New value AF is used to enter the table whereby a more accurate new value of GBF is retrieved. Both the newly obtained values of AF and GBF are then inserted as constants in the algorithm solver block (at S in  FIG. 5 ). 
         [0054]    An accessory table mount  90  is shown in three orthogonal views in  FIGS. 8-10 . It converts thread inspection tool  1  from a hand-held unit to one that can be conveniently used on a table or bench top. Table mount  90  has base  91 , threaded shaft  92  with knob  93  at its distal end, split clamp  94 , and adjustable front rest  95 . In operation, with clamp  94  loosened, thread inspection tool  1  is inserted through the circular opening and secured by tightening shaft  92  via knob  93 . Tool  1  is positioned so that its front end is in registration laterally and above adjustable rest  95  which is intended to be of aid in supporting the unit under test. 
         [0055]      FIGS. 11-13  relate to an alternate mechanical clutch embodiment of the compact ergonomic thread gauge of this invention. All of the components and operation of the depth adjusting subsystem (see  FIG. 2 ) of the previous embodiment have been incorporated into the front end of this alternate embodiment. This embodiment, however, relies on a mechanical adjustable torque limiting clutch to adjust and limit the torque applied to the thread gauge. 
         [0056]      FIG. 11  shows thread inspection tool  100  with thread gauge  2  at the front end, depth limit collar  3 , lock nut  4 , internal sleeve  25 , and reversing switch  70  which are part of the depth adjusting subsystem. Housing  101  contains all the major components. Battery  103  at the distal end is used to power the thread inspection tool. Membrane switch  102  has a clockwise and a counterclockwise activation element. Indicator  104 , typically an LED, is lighted when the inspection tool enters the automatic reversal phase when the depth limit is encountered. 
         [0057]      FIG. 12  shows more of the major internal components such as bearings  60 , torque limiting clutch  110 , motor  112 , PC board  114 , and battery board  116 . 
         [0058]    The flow chart of  FIG. 13  describes the operation of the alternate embodiment. The operation starts when the desired element of membrane switch  102  is pressed; this starts thread gauge  2  rotation. If the limit switch  70  is tripped, indicating light  104  is turned on simultaneously with the reversal of motor  112 . After thread gauge  2  exits the test element, the operator should release finger from the membrane switch to reset the tool. Note that operation will stop at any point if the finger is released from the membrane switch element; this is a safety feature. The membrane switch incorporates two normally open elements either of which must be continually pressed for operation. 
         [0059]    If the torque limit is exceeded before the limit sensor (switch  70 ) is tripped, the mechanical torque clutch slips. This is evident to the operator. At this point the operator will move his finger to the alternate membrane switch element to perform a manual reversal of the thread gauge to withdraw it from the test element. 
         [0060]    In the foregoing description, certain terms and visual depictions are used to illustrate the preferred embodiment. However, no unnecessary limitations are to be construed by the terms used or illustrations depicted, beyond what is shown in the prior art, since the terms and illustrations are exemplary only, and are not meant to limit the scope of the present invention. 
         [0061]    It is further known that other modifications may be made to the present invention, without departing the scope of the invention, as noted in the appended Claims.