This model allows for pressing the M2.5 T-Nut onto the M2.5 hex nut without it wriggling around from under the T-Nut.
I've had pretty good luck not using the T-Nut side, but sometimes it's a tight squeeze. In the event using the T-Nut side doesn't work using just your hands, there's a groove there to use a pair of channel locks.
Only once did that not work for me in about 50 T-Nuts and I figure that T-Nut just wasn't a team player.
For use with the TM2.5 T-Nut model here:
https://www.printables.com/model/228663-skadis-t-nuts-mounting-system-for-ikea-skadis-pegb
The author remixed this model.
This is an enhancement to allow mounting of the T-Nut and isn't necessarily a remix.