There are two different types of Apex bars (standard and oversized) and which kind you need depends on what the rest of your setup requires.
For a custom scooter, generally, the parts you need are:
- Clamp of some kind with associated compression mechanism that works with headset, fork, and bars
- Bearing spacers
- Wheel spacers (rear, unless brake has a carrier with built in spacers; some forks need wheel spacers as well)
- Grip tape