1) Glide Size
Glide size is determined by the OUTSIDE DIMENSION of the tube or leg. For inside fitting glides, also pick according to the gauge of the tube
2) Tips for "Safe Gliding"
Clean glides regularly. Often people will use glides (plastic caps or inserts) on the bottom of chairs. With proper care, they are considered excellent floor protection. They must be cleaned on a regular basis, since they can pick up dirt particles and scratch your floor.
Felt protectors are sticker-like glides that can be applied to the bottom of chair legs or other furniture. It is necessary to clean or replace as needed.
Replace any glides that are showing wear to prevent any damage to your floors.