The FLEX-FIT Duo MB343SPO is a lightweight yet durable 3.5-inch to 5.25-inch mounting kit bracket that utilizes a single standard external 5.25 computer bay to accommodate a 9.5mm Ultra-Slim ODD (optical disk drive) and a 3.5 HDD / device. This would ultimately maximize your system space, allowing the user to fit more devices into a smaller space.