5.25'' to 3.5'' adapter for HDD with fan and silencer

thingiverse

This is a 5.25 inch frame for 3.5 inch hard disk. You can add a 40mm fan for cooling the hard drive if you want. The outer side part is a silencer for the fan. It's a double "S" air duct that air enters from the sides and suppresses fan noice. You can also pass a piece of cloth through the duct for better results which in addition acts as dust filter.