The Radial J-Rak 4 (part R800 1016) is a 1U, 19-inch rack adaptor that holds up to four Radial direct boxes, splitters, isolators or Reampers side by side in a single rack space. It lets engineers and installers combine several units in one tidy, protected assembly for touring racks or permanent installations instead of leaving loose boxes on the floor. Mounting is simple: you remove the unit's outer shell and slide its inner frame into one of the four bays. Radial lists a wide range of compatible models, including the JDI and JDI Stereo passive DIs, the J48 and J48 Stereo active DIs, J33, JDX 48, JPC, ProAV1, ProAV2, ProD2, PZ-DI and Trim-Two, plus interfaces such as the J+4, J-Iso, JS2, JS3, LX-2, LX-3, Pro-Iso, ProMS2, Relay Xo, Highline Stereo and Twin-Iso, and the JCR and X-Amp Reampers. The rack comes empty: DI boxes are sold separately. For eight units, Radial offers the larger J-Rak 8.