Instead of using bearings in the fidget spinner arms, I chose to save the money (literally) and created a Fidget Spinner Wallet which uses (8) US quarters as the perimeter weights and side channels to hold paper currency.

As an added bonus, when the two halves are rotated 90 degrees, 2 coins are held in each arm creating a quad spinner configuration.

Step 1: Materials

3D printer and spinner files (Fusion 360 and STL files attached)
Blue painter's tape
Round file
Bearing, size "608" (8mm ID x 22mm OD x 7mm thick)
(8) US quarters and (2 or 4) pieces of paper currency

Optional (for Guide Pin)

Short piece of 1.75mm filament
Scissors or wire cutters

Step 2: 3D Printing

For this prototype I used PLA filament in a Printrbot Simple printer. Many people use the printer throughout the day, so the print bed often needs to be retaped before use. Rather than retape the whole bed, one simple "hack" that I use is to only tape the portion that I need as well as the 3 corners that the printer uses to determine the bed height.

Although the parts were printed without rafts or support material, some cleanup was needed to ensure a snug fit with the bearing. For the caps I simply used a small strip of tape to tighten the fit. For the main body I used a round file to open up the hole so that it was snug around the bearing, but still loose enough to allow the halves to be rotated open.

The Fusion 360 and STL files are attached below.

Step 3: Guide Pin (Optional)

My original design did not include side channels for paper currency, so I included a slot and guide pin to keep the halves aligned. A 3d-printed pin would be very weak, so instead, a short piece of 1.75mm filament is inserted and trimmed to length.

NOTE: PLA tends to be brittle and can break when bent, so I used ABS filament for the pin.

Step 4: The Finished Prototype

The wallet can hold up to (8) US quarters (5.67 grams each) and 4 sheets of currency. In "wallet mode" the spinner functions very much like a typical spinner.

To create a quad spinner, remove the bills and carefully rotate 90 degrees so that 2 quarters are held in each arm. In "quad mode" the quarters that hang down tend to get thrown if spun too quickly, but otherwise it functions like a typical spinner.

I do not have a video channel, so I have attached 5-second videos of the spinner in action, both in wallet mode and in quad mode.