Caster HQ's 7/8" Expandable Rubber Adapters are extremely easy to install in a variety of tubing sizes including both Round and Square Tubing. The most common application for rubber adapter casters would be commercial grade kitchen prep tables but these casters work in many different applications and tubing with a wide range of rubber adapter sizes. The rubber adapter works by expanding inside the tubing allowing the caster to fit tight into the legs or tubing on your equipment or table. We offer 8 different sizes ranging from 3/4" , 7/8", 1", 1-1/8", 1-3/16", 1-3/8", 1-1/2", and 1-3/4". These are the most common sizes for most industry standard inner diameter seen in equipment tubing or table legs. The round expandable adapters also work great in square tubing legs by expanding they will fill all gaps for a tight fit, sometimes you will need one size larger if going into a Square Tube. Round adapters actually work and expand much better compared to square adapters in square tubing. We do not recommend square expandable adapters and will always recommend round adapters for both round and square tubing. The Round Rubber expands more evenly in Square tubing versus a square adapter that is why we only offer round adapters for both Square and Round Tubing. Give it a try!