This is a bracket that positions a 40mm diameter cooling fan over the Pololu A4983 stepper drivers in the RAMPS (RepRap Arduino Mega Pololu Shield).
The fan used was a 40X40X20 12VDC FAN, RS Stock No. 544-0526 http://uk.rs-online.com/web/search/searchBrowseAction.html?method=searchProducts&searchTerm=544-0526&x=25&y=8
The fan is countersunk into the bracket and fixed in place by M3x30 socket screws.
Additional holes in the corners of the bracket line up with the mounting holes in the shield board. M3 stud, coated in PTFE tube (d3D4.5) to prevent any shorts, was used to position the bracket above the shield.
The fan can plug into the 12VIN and GND-IN pins just beneath D8 on the shield.
Print the bracket and clean out the holes using an M3 drill bit.
Countersink the fan into the bracket and bolt into place using washers to prevent damage to fan and bracket.
Cut M3 stud and PTFE tube to required length, allowing enough space for RAMPS wiring - I used 55mm length for the PTFE tube, 70mm for M3 stud.
Tighten a nylock M3 nut onto the end of each of the M3 studs, place through the shield, slot the PTFE tube over, washers, bracket, washers and finally plain nut.*
Connect the fan red wire into the 12VIN pin and the black wire in the GND-IN pin on the shield, just next to D8.
*Purpose of plain nut on top and nylock on bottom is so top plain nut can be tightened and the stud won't push through the bottom nylock into the Arduino Mega below.