While the official Pocket Operator silicone case offers basic protection from bumps, I wanted something stronger that I could toss into a bag and protect the knobs and contacts while traveling. This is a basic sliding box that is meant to hold the PO-33 with official CA-X case and lanyard. The tolerances are tight, so if you want a bit of a looser fit, scale the model up to 101% or 102%. I use the lanyard to remove the device from the box when I'm ready to pull it out.