sickle 25 and contains a bent portion 38 that slides over the upper surface of the inner knife sections 32 to maintain a vertically spaced relationship between the left and right sickles 21 25 during operation thereof it can be seen that the inner knife sections 32 are maintained in a shearing relationship with the inner knife sections 34 during operation of the cutterbar 20 to effect a severing of crop material along the transverse center of the header 10 the endmost inner knife section 32 can be inverted as is known in the art to provide a more precise shearing relationship at the inboard ends 23 27 of the respective sickles 21 25 referring now to fig2 5 it can be seen that the special threaded fastener 40 includes a head portion 42 adapted to the countersunk into the body of the inner knife sections 32 34 and defining one end of the fastener 40 while the opposing end of the fastener 40 is formed as a threaded portion 44 which is adapted to threadably receive a special hexagonal nut 50 the fastener 40 also includes an intermediate portion 45 positioned between the head portion 42 and the threaded portion 44 the intermediate portion 45 has a non circular cross sectional configuration while both the head portion 42 and the threaded portion 44 are circular in cross section the intermediate portion 45 is engageable with an opening 46 formed in the support bar 35.