All the features of 2 single wooden non-folding window cribs, but in a convenient space saving system!! Clear acrylic panels at each end of the crib allow a caretaker to watch little ones while they sleep or play in the cozy wooden window crib.Two 3" thick vinyl-covered foam mattress included and that are compliant with Federal Flammability standard 16 CFR 1633. Independent use possible by purchasing either the evacuation frame or caster accessories. When using either the evacuation frame or caster accessories the cribs cannot be used in the modular frame.Upper window crib features a swing down safety gate for easy accessibility and lower crib rolls out for caregiver convenience. Meets the Mandatory CPSC 16 CFR 1220 regulations for non-full size cribs. The optional ball bearing casters are attached to cribs by a Chicago bolt system. This is not only a stronger system but also eliminates the danger of exposed bolt threads. Add strength and sturdiness to the 755 crib for a fire drill situation with the additional purchase of a WC-504-EVA evacuation frame. When using either the evacuation frame or caster accessories the cribs cannot be used in the modular frame. Bilingual instructions in English and Spanish. Check with your local license dept to be sure this modular crib is allowed to be used in your area.