How to add dimension in batch rename

This should be close....

#target bridge 
if( BridgeTalk.appName == "bridge" ) {  
var menuDel = MenuElement.create("command","Add size to Filename", "at the end of Tools","Addcmtofilename"); 
}
menuDel.onSelect = function () { 
var sels = app.document.selections;
for(var a in sels){
var myThumb = new Thumbnail( sels); 
var Resolution = myThumb.core.quickMetadata.xResolution;
if(Resolution == 0) Resolution = 72;
var CM = Resolution /2.54;
var Height = (myThumb.core.quickMetadata.height/CM).toFixed(1);
var Width = (myThumb.core.quickMetadata.width/CM).toFixed(1);
var newFileName = Width.toString() + "x" + Height.toString() +"cm_" + decodeURI(sels.name);
sels.spec.rename(newFileName);
    }
}