WP Grid Counter Custom Loop

Hi Guys,

I am trying to create a grid loop for my portfolio section on my website.
I don’t want to use a plugin!
I want to display the portfolio listings in four (‘threecol’) columns.
On the 4th column in the row I need to add a CSS class of “.last”

Currently I have the following code.

<div class="row">
   <div class="container">
	<div class="full-width" role="main">

            //Here is where I would like to place the code.
            <div class="threecol <?php // if it is the fourth in the row add class LAST to it?> ">
            <?php get_template_part('loop');?>
           </div>
	</div>
   </div>
</div>

Hope this makes sense. I want to simply wrap each post in a class with threecol. On the fourth one (Or last in the row) add an additional class of last and start a new row and repeat as required.

Its really bugging me, I have found code snippets that give me the jist but can’t edit them to my needs, or the loop doesn’t close and it repeats over and over. HELP!!!!

Cheers

Dan