The steel threaded metal caster inserts are specifically designed to be inserted into Square legs/posts and offer a deep setting that will stay securely in place. Features a 5/16-18 thread that is commonly used with correspondingly stemmed casters and flush fittings offer a clean and simple finish. Designed to fit in 3/4 Inch Square tube (outside dimension) of multiple gauges (16 to 18 gauge). Allows casters to easily roll over thresholds, extension cords and more without being displaced and can be used in industrial, commercial and residential environments. Manufactured from a heat treated hardened steel that provides extra durability when properly installed. These square metal caster Inserts feature a hardened steel, double star design that inserts firmly into any Square Tubing or Square Leg and is not easily removed. The square double star caster inserts are specially designed to sit deep in the tube allowing equipped items to roll over thresholds, extension cords, cracks in the floors and more without fear of the connector slipping out. Our double star connectors work with any quality caster such as Outwater's extensive line of threaded wheel casters. These inserts are available in a variety of popular sizes and fit 16-18 gauge (approximately 1/16" to 1/8" walls). The edges of the connector fit flush to the outside edge of the tubing for a clean, finished appearance.