These light-duty plastic casters are on swiveling stems and have dual 1-1/2" dia x 5/16" wheels in 1-7/8" x 1-3/16" hemispheric housings. Stems are striated steel, 3/8" dia x 3/4" long. We're thinking these would be fine for your average chair. Our each is a bag of (4).

Good-bye backaches. Save your sacroiliac with a 3-wheeled professional mover's dolly. It measures 6-3/8" wide between a trio of swivel casters with 1-9/16" x 11/16" wheels, and has a drop-down center and a 1/2" dia hole for permanent attachment to frequently moved items. Steel construction, 110 lb max load (so not piano-duty), and rubber pads above each wheel. Stands 2-1/2" tall. We think ordering (4) would be a good place to start.

The ball casters are great swivelers and quite snazzy looking, too. Seen on your better chairs everywhere. These are brass plated on 1-1/2" square mounting plates with 3/16" holes at the corners. 2-1/2" dia.

These small swivel plate casters have dual 1-3/8” dia plastic wheels on coincidentally 1-3/8” square mounting plates with (4) holes. Measure just under 2” tall and are screaming to be used to make rolling plant holders, because nothing is more boring than plants that just sit there in one place all the time. They have a little dirt on the wheels that cleans up nicely with some soap and water. That's Surplus for ya'.

Our 4" dia swivel-stem casters have 3/4" wide dual black-plastic wheels and 1" steel stems with 1/2" - 13 threads. Available with or without a foot-operated lock No weight limit listed, but they're pretty sturdy, and pretty snazzy, at least to the extent that casters admit of snazziness.

These ball casters are great swivelers and quite snazzy looking, too. Seen on your better chairs everywhere. These are brass plated, 2-1/2" dia on 1-1/2" square mounting plates with 3/16" holes at the corners.