This is a different approach from our first hexagon adapter. This version is more optimized and comes in 2 different versions. You can either use DIN EN ISO 4032 hexagon nuts or DIN 562 flat square nuts to install the 25x25mm fan or the adapter from 25x25mm to 40x40mm. As bonus we made a stylish fan grill 40x40mm to protect the fan. You can find a more complete description in our StoutWiki: http://wiki.stoutwind.de/doku.php?id=stoutwinds-hexagon-hotend-addons