The Wooden Camera Advanced Cage Kit for the Blackmagic Camera, a kit from B&H, combines a multi-threaded cage with several accessories to form a complete tripod mount rig for the Blackmagic Camera.
A top handle, also multi-threaded, attaches to the top of the cage (or you can attach it directly to the top of the camera), and a mini baseplate, with 1/4" and 3/8" tripod-mounting threads underneath it attaches to the bottom. The baseplate features a 15mm rod clamp connected to its front, and a second, identical clamp, is included with the kit for attachment to the rear. Both clamps accept 15mm rods. You can have a pair of rods extending out from the front, and another pair from the rear. Two 15mm rods, 15 inches long, are included and complete the kit. You can attach these rods to the front 15mm clamp and mount a follow focus and matte box onto them.
If you will at some point add more components to the rig, and the addition of these components will outfit the rig with rods elsewhere than on the baseplate, then you'll be able to mount the second included rod clamp onto these rods and attach battery plates or cheese plates or similar accessories to it. The clamp features threads running along it for just such purposes.