blade 30 follows a different pivoting and or translating movement path spring element 51 comprises contact portion 52 interfering with blade 30 along at least a portion of the pivoting and translating movement path of blade 30 in some embodiments according to this invention as blade 30 moves along the pivoting and translating movement path between the retracted position and the expanded position such as shown from fig5 to fig6 for example distance 62 is varied between a shaft axis such as center axis 41 of shaft 40 and a contact area 67 formed at near or between contact portion 52 and blade 30 and or body 20 and or any other suitable structure or element directly or indirectly connected to blade 30 and or body 20 in some embodiments of this invention spring element 51 contacts shaft 40 at or near opening 58 and spring element 51 has a lock surface engageable with body 20 and or any other suitable structure to prevent movement of spring element 51 with respect to body 20 as blade 30 follows the pivoting and translating movement path fig2 and 22 show expandable arrowhead 10 according to one embodiment of this invention in this embodiment o ring 75 is used in lieu of spring element 51.