Fan Duct for 40mm fan on E3D v5 barrel

This fan duct allows for using a 40mm axial fans, which are easier to find than 30mm fans and seem to last longer anyway.

If you're using a 40mm fan to improve cooling, be sure to also use computer thermal paste on the threads of the heat break's upper end. That will probably help at least as much as this fan duct does.

The fan duct clips onto the barrel without any extra hardware. For me, it seems to stay put, stays aligned and doesn't rattle, and easily pops off with gentle but firm forc