https://www.gobilda.com/2302-series-aluminum-mod-0-8-hub-mount-gear-14mm-bore-105-tooth/ The 105 tooth, MOD 0.8 gear will mate with any MOD 0.8 gear, but when building on pattern, the most common partner for this gear is a 15 tooth pinion gear or servo gear.  Using the pinion gear you can create a 7:1 underdrive or overdrive setup depending on your application.  When used with the 15 tooth servo gear, the combo creates a 7:1 underdrive, slowing the final speed while increasing the torque by 7x.