These mount on either end of your GlowForge Gantry. There are three on each end, six total.
GlowForge does not sell these as a spare part. when one or more fails, it’s $1600 for a refurbished laser.
GlowForge Gantry Wheels are made of urethane. Mine are made of much more durable POM/Delrin and will probably last your lifetime. They are NOT standard 3D printer wheels, those have a 5mm center.
They each come assembled with the correct bearings. Sold each.
Laser not included 🙂