There is a part called MGN12 Carriage Holder that you can slide the second carriage onto and wrap up with some leftover plastic wrap. Be careful here not to lose any ball bearings by having the carriage come off of the rail or holder even a little bit.
Look in the slots to ensure the T-nut pin rotated fully as well. I had to manually turn it by sticking something in the slot and completing its rotation.
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The NIDEC W40S12BS2E5-57T04HF9 4028 Fan has a white wire for the Tac instead of the shown yellow wire.
There is a part called MGN12 Carriage Holder that you can slide the second carriage onto and wrap up with some leftover plastic wrap. Be careful here not to lose any ball bearings by having the carriage come off of the rail or holder even a little bit.
Look in the slots to ensure the T-nut pin rotated fully as well. I had to manually turn it by sticking something in the slot and completing its rotation.