This is a remix of
"Ultimate 38mm Rotating Spool Holder - MakerBot Replicator 2" by jprikkel. Thanks so much for sharing this design!
I really liked his design and wanted to use it on my M2 so here it is. Pictures show step-by-step instructions and also a parts list using part numbers from McMaster-Carr.
I've included the Cubify Design files in case it needs modification and S3D factory file.
I used ABS 4 layers at .2mm with 70% infill. In the S3D factory file I have it set to "Use random start points for all perimeters. The reason being that if set to the "Optimize" option it would leave a seam on the spool holder which acted as a speed bump and would cause the reel to spin a little quicker than it should. Going to random eliminated that issue.
Please note that the original spool holder file from jprikkel will not work with this mount since I did modify it, so you would need to print both pieces.
The holes for the clips are designed so that the flat side of the clip is placed closest to the spool. There is an indentation inside the holes for the clip to "snap" in.
Also thanks to "markb" from Makergear forum for making me aware of this great spool holder!
VERSION 1.2 - Added grooves to the spool holder. (Note the pictures are from the original version which did not have the groove, the CAD picture does show them.) These groves allow for the use of reel adapters. Included in the files is an adapter with an outside diameter of 52mm. You will need to print two of these, one for each side of the reel (If you have reels with this size opening. These are a remix of http://www.thingiverse.com/thing:504298 by trevorjb. Thanks Trevor! I will add more adapters as I run into additional reels with different hole sizes.
One additional note I failed to mention. The spool holder is very tight initially on the bolt. You will need to use a heavy wire brush to ream it out. But this assures a nice smooth fit on the bolt after you do one pass with the wire brush.

03/03/2015: Added the Taulman3D 1lb Spool adapter

Please see the images for assembly instructions and parts list from McMaster-Carr