1) Glide Size
Glide size is determined by the OUTSIDE DIMENSION of the Tubing or Leg. For inside Fitting Glides, also state gauge of the Tubing.
2) Tips for "Safe Gliding"
Clean glides regularly. Often people will use glides (plastic caps or inserts) on the bottom of their chairs. Glides are considered to be good floor protection, however, they must be cleaned on a regular basis or they will pick up dirt particles and scratch the floor. It is also a good idea to replace glides periodically.
Replace your felt protectors. Felt protectors are sticker-like glides that can be applied to the bottom of chair legs and other furniture. It is necessary to clean or replace them often because they also collect dirt particles that will scratch the floor.