I really like the "Captive Nut" idea, and I make a lot of gears, so I thought I would combine them in this print.
I didn't use the Cura plugin to pause the print. Instead I monitored the percent status on the Anet display, and paused at 65% to insert the M3 nuts. I had calculated the layers in Cura (I think it was layer 46 (of 69 total) just before it would start to close the hex pocket). Worked great.
I modeled this in Fusion 360 with the Helical Gear generator, then modified it with the hex pocket and thru hole. The pocket is 0.1" deep (2.54mm) and the M3 nuts I used are .093" (2.37mm). This is to make sure you can insert the nuts fully and be below the print layer that will cover it. Make sure the nuts are pushed in as far as they can go before resuming the print, otherwise you risk running over the steel nut and damaging the print nozzle! (I learned this the hard way).
Thanks to Ratm3at for the inspiration to try this!
Goes great with the Spring Bushing by Puddlefist!
1.75 Green PLA by AIO Robotics
Temp: 200 / 60
I beveled the teeth corners in my model so I didn't have to sand off any sharp edges.
Had to open the holes a little with x-acto knife.
Otherwise used as printed.
Fusion 360 has a great Helical gear generator add-in.
Helix Angle: 30 Deg.
Pressure Angle: 20 Deg.
I played with the Module until I got the outside diameter to ~0.71". Small enough to clear the rear frame of the Anet A8.