PURPOSE: To provide effective horning of various gears by a method wherein a horn proper with spiral ridges is formed with a hard material, of which surface is furnished with a layer of grinding grains, while the horn is made detachable from a sleeve fixed to the rotary shaft to facilitate replacement.

CONSTITUTION: A horn proper 24 with a layer of grinding grains 27 on its threaded portion is elastically supported by supporting rings 21, 22, 23 composed of elastic material. The layer of grains is formed with grains such as CBN, etc. using any kind of binder. A horn 11 consists of the horn proper 24 and a sleeve as a separate body and they are fastened by a double nut 15 together. When the nut is loosened, the horn 24 can be replaced simply with another with ridges having a different module or a layer of grains of different grain size.