DJCRAWLER 58mm Omni Rack Easy Wheels (S1 level) for Brompton Folding Bike & Electric Bicycle, 10KG Load Omni-direction Roller Replacement Accessories with Bearing [M6*45MM/60MM Screws] (white)

On each large white wheel there are two of the small black wheels which do not spin freely and have a large amount of friction. I bought these for a hobby project that requires minimal friction. I had to take them apart and file off these nubs, presumably left from poorly controlled molding process. After that they worked fine

Used these for the first time today and was pretty pleased. I mounted them on the rack because they're a bit wider than the rollerblade wheels I was using and my heels barely clear those when pedaling. They make turning in shopping cart mode much easier and more stable. They roll pretty well on concrete and lenoleum, and do ok on asphalt. They're a little noisy but it's not too bothersome. The package also came with a few spares of each part. They seem like they'll last if you take care of them.

But after two months the little Omni wheels broke off. Clearly they don’t hold up in Bostons cobblestone streets and that’s something to keep in mind.