The iFixIt extension is printed in two parts and then glued together after printing. The final length of the extension after joining and it is inserted in the iFixIt screwdriver is 65 millimeters. 

I glued a small piece of steel (like a shim) to the end of the 4 millimeter bit that goes inside the screwdriver to make it magnetic. 

The geometry of the extension shaft was created by forming a hex and filleting the corners, except for two so that the part can still be printed flat. 

I strongly recommend printing flat with 100%  solid infill and a small layer height, using Bambu Lab's Polycarbonate. 

I know a metal extension would be ideal, but this worked for me. There was a fan that needed cleaning and I did not have a long screwdriver that could do the job.