There are (4) Flush racks included with your ATC order. They are suitable for most situations but are provide the best bet for success when it comes to utilizing one of our Z Independent boots (currently on the V9 has been validated, although the V3 shows potential). The height of the boot will need to be above tool holder in position regardless of its positioning. With a Z Independent boot, lateral spacing of the holders/racks is not of concern, and can be in any location as close or far as you'd like without any consideration. Again, the consideration is how much vertical clearance you have. Unlike our tall or short racks, the entirety of the holder's lower half is below the worksurface. Considerations with Z Dependent boots such as the V7 or V10 would be that the spindle is able to reach the spindle without contacting the surface. Contacting the surface would reduce this capability, and a Z-Dependent boot would be better suited for a Tall or Short to give it that extra elevation.