The trays come in three sizes: ATX, EATX, and 4p/MEB/SWTX.
All of the trays can be stacked with the purchase of two additional posts (all necessary fasteners are included).
ATX Open-frame Tray
The open frame ATX size tray measures 8.75 x 17.75 x 10.75-inches (H x W x D).
With the addition of an optional lower tier, the tray becomes a full-blown tech/test station/bench:
Drives are mounted to the rails via rubber grommets that are attached to the drives with button head bolts (M3 for SSD/OD and #6-23 for 3.5-inch hard drive):
In response to the video review by LinusTechTips, the tech station has been improved with added support beams for the PSU and a radiator.
EATX Open-frame Tray
The open frame EATX size tray measures 8.75 x 17.75 x 14-inches (H x W x D).
EATX-size tray with optional lower tier (along with an optional drive cage):
4p/MEB/SWTX Open-frame Tray
The MEB/SWTX size tray measure 9.75 x 23.5 x 16.25-inches (H x W x D).
4p/MEB/SWTX Open Frame Tray
The open frame MEB/SWTX size tray measures 9.75 x 23.5 x 16.25-inches (H x W x D).
Options for open-frame tech trays
Hard drive mounting rails