I did not like the washer stack that comes with the default Proforge 3 build.. But to buy actual idler pulleys was going to cost a good bit, plus it will require drilling and tapping the frame for the correct shoulder bolts. So instead, I took the old school RepRap approach, and used stacked flanged bearings. I used F604ZZ (4x12x4mm shielded) bearings, but you can use F604-2RS if they are more available to you. You will need 24 bearings so you can double stack them to make 12 idler pulleys. With these exact bearings, you can use the hardware that came with the Proforge. You need to use some of the washers, but you will have a lot left over. I took pictures of each stack, side-by-side. Pay close attention to where the washers go so you get everything aligned properly.