The 18x6x12-1/8 forklift tire is a solid press-on tire which go on press-on rims aka industrial wheels. The rubber type of solid press-on tire is often called a "cushion tire", as the rubber tire allows for a built-in cushion compared to their even more solid counterpart, the polyurethane press-on tire. 18" Tall, 6" Wide bonded on 3/8" steel press-on ring and will mount on a press-on type 12-1/8" wheel. The ID is +/- 5/1000th of an inch.