flutes varies as described above the width f of the flutes and the width l of the lands 30 will inversely vary somewhat along the length of the pilot end portion for example in the above example the width f of the flutes is about 0 03 inches and the width l of lands 30 is about 0 005 inches at the upper end of the working length adjacent the handle 14 and the width w is about 0 025 inches and the width l is about 0 01 inches adjacent the pilot end 16 as will be apparent the width l of the lands 30 is equal to a significant portion of the pitch p which is preferably equal to at least about 15 of the pitch p in the above example the width l varies from about 14 2 of the pitch p adjacent the upper end to about 28 5 of the pitch p adjacent the pilot end 16 this is desirable in that the relatively broad lands 30 prevent undue cutting by the instrument laterally into the wall of the canal during manipulation of the instrument by the dentist fig5 illustrates another embodiment of the invention which is similar to the above described embodiment with the exception that the peripheral surface of the working length is cylindrical rather than tapered fig6 illustrates another embodiment where the peripheral surface of the working length is.