SO fiddle

Test Fiddle mainly for SO Questions

by Nick Craver

HTML

<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.4/themes/overcast/jquery-ui.css">
<div class="content">
<form>
<div class="item">
blablaform stuf
</div>
<div class="item">
blablaform stuf
</div>
<div class="item">
blablaform stuf
</div>
<div class="item">
blablaform stuf
</div>
</form>
</div>

CSS

.item { border: solid 1px #ddd; }
.wrapper { border: solid 1px red; padding: 2px; }

JavaScript

jQuery.fn.wrapSet = function (interval, wrapElem) {
  for(var i = 0; i < this.length; i+=interval) {
    this.slice(i, i+interval).wrapAll(wrapElem);
  }
  return this;
};

$(".content div.item").wrapSet(2, "<div class='wrapper'></div>");