5000 CR/ECR Certified Class 10 Cleanroom and ESD/Cleanroom models Exceeds ANSI/BIFMA* standards 12-year guarantee Heavy-duty dual wheel casters for hard floors. Hard plastic dual wheel casters for carpeted areas. “02” Control with separate levers for seat and back tilt. (Specify model with “02” option, ie: 5502) Additional lumbar back support. (LBS) Ergonomic adjustable armrests with polyurethane arm pads. Larger 20” diameter adjustable chrome foot ring for models 5300, 5301,5500 and 5501. Larger ergonomic seat. (20”W, 18”D, 3” Thick) Larger backrest. (17 1/2”W, 19”H, 4” Thick) Customized options available.    4000 CR/ECR Certified Class 10 Cleanroom and ESD/Cleanroom models Exceeds ANSI/BIFMA* standards 12-year guarantee Heavy-duty dual wheel casters for hard floors. Hard plastic dual wheel casters for carpeted areas. Larger 20” diameter adjustable chrome footring for Models 4500 and 4501. Mushroom glides for Models 4200, 4201, 4600 and 4601 (add 1” to seat heights).