50mm to 40mm fan duct.

thingiverse

We have designed this fan duct specifically to convert your existing 40mm fan into a more powerful 50mm fan. It is essential to consider, however, the added space required by this larger fan unit. Changing Over Your Fan: Since I had been saving a spare 50mm fan for some time, I decided it was finally the right moment to switch to this more efficient cooling device. Fortunately, my existing setup can accommodate the 50mm fan since both units share the same voltage requirements.