It’s a pillowblock with a bearing inside, and what makes it interesting to me is that it includes two set screws to hold the shaft, and that it’s inexpensive and pretty convenient to use. It saves me having to build a bunch of pillow blocks and use shaft collars.

It’s meant to be a mechanical stand-in for designing a machine, the mount faces, hole locations, hole sizes, offsets, relative positions and bores are reasonably accurate. I did work it into a reasonably faithful looking model, though it’s not a perfectly faithful in a few places that don’t matter for making a mechanical design.

These (or most likely, clones of these) are available cheaply on Aliexpress (Alibaba), eBay and Amazon.

I previously mislabelled this part as PK000.

See http://www.thingiverse.com/thing:878151 for KP001, the 12mm version.