My thoughts went to bearings while contemplating a mechanical project. I have the luxury of adjusting the design to fit a bearing thanks to the wonders of 3D printing. Given this flexibility, the obvious first path to investigate is to learn where to get bearings - cheap!

I've learned to not kill myself on a roller blade some years back, so I started looking for roller blade bearings based on the logic that there's enough roller blade production volume - and each pair of blades use 16 bearings - to drop the price of bearings. I quickly found that skateboard wheels use the same size bearing, then I learned that fidget spinners also use the same size bearing.

Eventually I realized I had the logic backwards - these bearings are not cheap because they're used in skates, they are used in skates because they were cheap. These bearings have been around far longer than any of those consumer products.

The industrial name for these mass volume commodity bearings seems to be "608". The 60 designate a series (Google doesn't seem to know the origin of this designation) and the 8 designate the interior diameter of the bearing. Letter suffixes after the 608 describe the type of seal around the bearings but does not change the physical dimensions.

Another misconception I had from roller blade advertising was the ABEC rating. It has come to imply smoother and faster bearings but technically it only describes the manufacturing tolerances involved. While higher ABEC rated bearings do reduce the tolerance range, that by itself does not necessarily mean faster bearings. There are more variables involved (the lubricant used inside, etc) but somebody decided the mechanical engineering details were too much for the average consumer to wade through, so its meaning was distorted for marketing. Oh well, it's not the first time that has happened.

Such details may or may not be important, it depends on the project requirements. Strict project demands (temperature, speed, load, etc) will require digging deeper for those details. For projects where pretty much any bearing would do, the 608 designation is enough to guarantee physical dimensions for CAD design and we're free to order something cheap. Either off Amazon (~$25 for 100 of them. Disclosure: As an Amazon Associate I earn from qualifying purchases.) or for even larger quantities, go straight to the factories on Alibaba.