Unknown mower.

[StarTech]

 

[Fish]

I don't know, it has the same part number on it as the other version with the lip, so it likely is incorrect.
I just did an image search.

 

[troy-built]

When you do replace the gear and what ever else is worn out be sure and grease it from time to time and it won't wear out again. While your working on your mower why not go over it and grease everything. Your mower will thank you.