When the 'teeth' of a GEAR WHEEL are separate and replaceable they are called COGS. May be wooden (or metal). Need to be a resilient close-grained wood. Woods used: Apple, Beech, Pear, Hornbeam, Oak, Acacia, Hawthorn, Holly, Ash and Oak often being used for wet work. Wooden COGS, the SHANKS of which are fitted tightly into MORTISES in the rim of the wheel after the fashion of a TENON, are secured by wedges or pins after the fashion of TUSK TENONS.