Injection molded FAULTLESS Polyolefin Wheel Casters are far stronger (200% better impact strength) than normal rubber wheels. Less expensive than rubber too! Highly resistant to most solvents and chemicals. Impervious to water, grease, oil, and gasoline. Self-lubricating and non-flattening. Can be steam cleaned. Double ball race. Plain bore. Each 4x1-1/4", 5x1-1/4", 4x1-1/2", and 5x1-1/2" wheel is straight sided. 71702 has 1-3/16x4" mounting holes.