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).

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.

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.

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.