<li<%= ' class="active"' if current == "Parts" %>>
  <%= link_to t("parts"), admin_product_parts_url(@product) %>
</li>

<% if @product.assembly? %>
  <% content_for :head do %>
    <script type="text/javascript">
      jQuery(document).ready(function(){
        $("ul.product-menu a:contains('<%= t("variants") %>')").parent().hide();
        $("ul.product-menu a:contains('<%= t("option_types") %>')").parent().hide();
      });
    </script>
  <% end %>
<% end %>

<li<%= ' class="active"' if current == "Parts" %>>
  <%= link_to_with_icon 'icon-sitemap', t("parts"), admin_product_parts_url(@product) %>
</li>

Use an icon for the Parts tab
Use an icon for the Parts tab
