I have had my 8.4 radio out so many times, I should know exactly what it is, but never looked that close under it. I know the square rubber insert does have a area on at least one end that sits in a slot. I took out the ra3 8.4 radio stock in my 13 Outdoorsman about 10 times back when truck had 30k miles, then upgraded to a ra4 2015 nav/hd radio one. Took the 2015 radio out about 10 times to install sub amp( took a year to finally listen to people here and buy a amp pro ch41) was best thing I bought and found it open box on Amazon for like $130. Before that I tried regular loc, ax dsp, a audio control one that adjusts for bass cutoff etc) amp pro was only thing that worked great. Then last week installed a antenna fakra amplifier(made improvement on picking up stations by like 30% for $10. Will be removing stereo again to wrap the upper and lower console.