It looks like this Part has been superseded by LEGO Part 10928 Technic Gear 8 Tooth [Reinforced].
Click on a colored part below to see the Sets and MOCs that use part 3647 Technic Gear 8 Tooth in that color. You can find an overview of all LEGO Colors here.
If a color is missing, it probably needs to be added to a Set Inventory.
This part has been used by MOCs in the following colors but not officially released.