Durable, weatherproof, dent proof, and rustproof. No sharp edges. Combine units for added height. Units are predrilled for easy installation, and can be bolted together. Inside dimension: 37" with 16" projection. Use bubble window well cover model No. W4217-DI, W4218, W4018-DIB, or low profile window well cover model No. 4017CH-DI or W4418.