other tool can then advance the extraction screw which advance has the effect of backing the retainer 14 out of recess 18 as the retainer 14 moves outward an edge of the planar upper surface 42 of the retainer 14 comes into contact with the laterally extending surface 40 located immediately above the retainer engagement feature 26 consequently the outward movement of the retainer 14 forces the associated cutting bit 12 from the drum 10 fig6 is a sectional view of a drum 10 similar to fig4 showing a removable insert 65 having internal threads 66 designed to engage the fastener 58 securing the retainer 14 in place in the recess 18 the removable insert 65 can have an outer engagement surface 69 designed to cooperatively engage a corresponding interior engagement surface 71 in opening 60 the cooperatively engaging surfaces 69 and 71 can be for example threads preferably of a different pitch than the internal threads 66 engaging the fastener 58 and possibly of a hand opposite that of the internal threads 66 the removable character of the insert 65 ensures that the drum 10 can quickly be refurbished in the field if necessary in the event of any damage to the fastener engaging threads 66 this avoids the necessity of having to.