in fig1 is illustrated a typical shearer pick 1 in common use , worldwide , comprising a non - circular shank 2 adapted to be releasably located within a corresponding aperture in a tool holder or pick box , and releasably retained against inadvertent loss by a latching means , such as a multi - ribbed , synthetic plastics insert in the double “ o ” aperture 3 . at a front or leading face 4 of the shank 2 is provided a blind aperture 5 to receive an additional , or alternative , resilient , shank retaining button ( not shown ). from the upper end of the front face 4 of the shank 2 a forwardly directed enlarged shoulder 6 extends having an underside 7 to seat on a support surface ( not shown ) of the associated tool holder or pick box in the well known manner . further forward , the shoulder 6 is provided with a notch s for engagement by an extraction tool , such as a screwdriver or drift , when extraction of the pick 1 is required . at a trailing face side 9 of the shank 2 is provided a heel 10 also having a support surface 11 , and in addition a through hole 12 to accommodate a portion of a water spray nozzle ( not shown ). beyond the shoulder 5 and heel 10 extends an integral blade 13 provided with a carbide tip 14 . shoulder 6 , heel 10 and blade 13 comprise the head 22 of the cutter tool 1 . in accordance with a first embodiment of the invention , a slot 15 is provided in cutter tool 1 a at a 90 ° junction between the leading face 4 of the shank 2 and a portion 16 of the enlarged shoulder 6 . in this embodiment , the slot 15 extends at a 45 ° angle to the front face 40 of shank 2 and to the underside surface 7 of shoulder 6 . slot 15 is provided to influence that the cutting tool 1 will break the head 22 from the shank 2 so that the shank can be removed downward when used in a tool holder that provides a removal opening such as disclosed in british application serial no . 1113669 . 4 field aug . 9 , 2011 . fig2 a discloses a preferred slot formation at the junction between the shank and the shoulder . in this embodiment , slot 15 a extends inward at the junction along the top of shank 4 to define a frangible portion 20 that is sufficiently robust to withstand normal operation , but will break when the cutter tool 1 b strikes a steel member or other hard object . the provision of slot 15 a dictates that the cutter tool when striking a steel member will , in most cases , break cleanly along the top of the shank without bending or distorting the shank 2 or leaving a portion of head 22 remaining connected to the shank . an unbent shank can be easily tapped downward and out of the tool holder for tool holders with a lower removal opening such as disclosed in british application serial no . 1113669 . 4 filed aug . 9 , 2011 . slot 15 a extends from a front surface 24 of the cutter tool 1 b . in one preferred embodiment , slot 15 a extends perpendicular to front face 4 and opens only in the front surface ( i . e ., in the direction the tool is driven during operation ) of the cutting tool , which in this embodiment is the front face 4 of shank 2 , and in the sides to its depth of extension into the tool from the front face 4 in order to more effectively provide a clean break without distortion of the part remaining in the tool holder ; i . e ., it is considered beneficial for directing a clean fracture for the slot to open only or primarily in the surface which receives the primary loading . slot 15 a defines a frangible portion 20 in the remaining thickness of the material . frangible portion 20 is formed to resist normal loading and remain intact during normal operation of the cutter tool , and to provide a clean break of the head 22 from the shank 2 without distortion of the shank when a steel member or other hard object ( e . g ., a steel member ) is struck . the minimum and maximum thickness will be determined based on the intended application as well as the design and material of the cutter tool . as stated previously , a not uncommon occurrence is for the blade 13 to strike a steel obstruction , such as a roof support bar , or buried tramway rail or pipeline . in this situation , the provision of the slot 15 or 15 a is aimed at propagating a break from the slot to completely separate the head 22 from the shank 2 without distorting the shank for easier removal of the shank from the tool holder . in another embodiment illustrated in fig3 , a slot 17 is provided in a front face 18 of the blade 13 in a zone 19 where the blade 13 meets the enlarged shoulder 6 . as with the earlier embodiments , the slot 17 preferably opens only in the front face of the cutting tool , which in this case is the front face 18 of blade 13 , and in the sides to the depth of the slot into the head 22 . as with the earlier embodiment , the slot forms a frangible portion 26 having a certain thickness . the frangible portion 26 has a certain “ dynamic strength ,” which is defined as the force required to break the frangible portion when the force is an impact load applied to the tip of the cutter tool . the dynamic strength of the frangible portion is , then , a factor of ( i ) the cross sectional size of the frangible portion where the break is intended ( typically the most narrow cross section ), ( ii ) material of the cutter tool at this cross section frangible portion , and ( iii ) the vertical distance between the frangible portion and the tip where the impact load is applied during use . in accordance with this one aspect of invention , the dynamic strength of the frangible portion 26 is less or weaker than the dynamic strength of the interface between the head 22 and the shank 2 . in a preferred embodiment , the dynamic strength of the frangible portion is at least about ten percent less than the dynamic strength of the interface between the shank and the head in order to reliably ( i . e ., in most cases ) direct the breaking of the cutter tool along the frangible portion rather than the shank - head interface when the cutter tool strikes a steel member or other hard member . in this way the shoulder 6 and removal notch 8 are preserved even if a steel member is struck by the tip 14 of the cutter tool to enable removal of the shank 2 from the tool holder so that a replacement cutter tool can be inserted . the dynamic strength of the frangible portion could be much less than 10 % weaker than the shank - head interface so long as the frangible portion remained intact during normal operation . in alternative constructions ( not shown ), a zone of weakness or frangible portion can be defined by means other than a slot defined in the cutter tool . in addition , other kinds of slots can be used even though they are formed in ways other than disclosed above . for example , a slot can be formed around the periphery or by being partially formed in both the front and the rear surface . in these alternative slot constructions , the slot is preferably primarily formed to extend from the front surface , i . e ., that the majority of the depth of the slot extends from the front surface . the slots 15 , 15 a , 17 are shown as narrow and linear gaps in the cutter tool , which is the preferred construction . nevertheless , the slots could have a non - linear configuration , have a wider ( not narrow ) width , and / or have an irregular shape . the term “ slot ” is intended to have a broad construction to define a gap in the cutter tool having a wide variety of possible shapes . the shape or size of the opening can vary considerably .