There are NOT ENOUGH FASTENERS to "Insert an M3x12 screw in each of the holes on the linear rail". Best you can do is every other hole (although that may be too many as well!)
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I've broken (3) belt grabbers trying to get the 5mm locking hex nut to pull into its cavity. I succeeded with ONE. Printing more now :(((
I also agree - install bearings before mounting the constraint brackets
There are NOT ENOUGH FASTENERS to "Insert an M3x12 screw in each of the holes on the linear rail". Best you can do is every other hole (although that may be too many as well!)