Check the listing for details. Radial J-Rak 4 4 Space Rack Adapter. Condition: New. Listed at 154.99 USD. Clean up your studio by rackmounting your Radial DIs. The Radial J-Rak 4 is the perfect solution to help keep your studio cleaner and more organized. This 1U rack shelf holds up to four Radial JDI-sized interfaces. With the turn of a few simple screws you can mount your DIs into the J-Rak. House all of the DIs for your session in one convenient rack shelf. The J-Rak is great for studios or permanent rackmount installations at venues. You can front or rear mount each unit to access the inputs and controls you need.