A cutting tool has an indexable insert, a holder with a holder member and an arrangement for securing the insert to the holder. An upstanding holder wall and a conical insert clearance surface are designed so as to enable securing of the insert to the holder in a finite number of fixed relative positions. A curved portion of the upstanding holder wall supports the conical clearance surface laterally in each fixed relative position of the holder and the insert. A tight abutment of the conical clearance surface on said curved portion is provided to dirt from penetrating therebetween.