Wanhao Duplicator 6 / Monoprice Maker Ultimate Dual Motherboard Fan Holder (60mm Fans) with extended feet (5, 8, or 10mm) to clear the blue relay. An iteration on a design by mentalbob and improved by PIYIRIO.
I use the extended feet here and remove the bottom cover to get airflow and clearance.
I was having a severe layer shift issue before this modification.
I used these fans (GDSTIME 60mm 24v Fan Dual Ball Bearings 6010 DC Brushless Cooling Fan):
And these cheap screws (iExcell 100 Pcs M3 x 30mm/35mm/40mm/45mm/50mm Stainless Steel 304 Hex Socket Button Head Cap Screws Bolts Assortment):
A dab of hot glue on connections and screws is a good idea.
The 60mm x 60mm x 10mm 24v 2pin xh2.5 fan above with ball bearings may not be available anymore.
Here are some other fan options: