12 HDD bearings of the type in the photo. They are very common. About 200 g of PLA or ABS. You'll need to print one base, two each of arm1 and arm2, and four of the roller vases. The bearing holes in the arms and the roller vases have to be correctly sized to press fit the bearings, so print the test block which has different sized holes and see which one fits your bearings. You may have to modify the hole sizes int he CAD file to get it just right. The rollers print one at a time using Slic3r's spiral vase mode so there won't be any seams or bumps in the surface. I used a 0.6 mm nozzle and set line widths to 0.75 mm, printing in 0.3 mm layers.