slop=0.5;

prongthick=5;
prongwidth=5;
ratchetstep=10;
ratchettooth=3;
ratchettoothheight=5;
overlap=0.5;

armendwallthick=2.5;
armendbasethick=1.2;

module ArmEnd(length=100){
  channelwidth = prongthick + slop;
  channeldepth = prongwidth + ratchettoothheight;
  totalwidth = armendwallthick*2 + channelwidth;
  totalheight = channeldepth + armendbasethick;
  difference(){
    translate([0, -armendwallthick, -armendbasethick])
      cube([ratchetstep+overlap, totalwidth, totalheight]);
    translate([-1, 0, 0])
      cube([ratchetstep+overlap+2, channelwidth, channeldepth+1]);
  }
}

ArmEnd();