A spool arm I made for the Replicator 2 (but you you edit the connection you should be able to mod for any printer).
Basically I wanted an arm which used bearings for minimum friction, with the added requirement of being able to replace bearings if I needed (can't imagine why, but I like over engineering).
Also tried a new enlarged section of the arm for easy reel removal while still keeping the reel in one place.
Made for reel internal diameter ~ 52mm, ~7cm wide. Made for 12 x 28 x 8mm bearings.
I used: http://www.ebay.com.au/itm/140907282542