Rail kit contains left and right rails (2 rails included). For installation in rack cabinets with mounting holes spaced 23.5" to 36.5" (595 to 936mm) apart. Maximum load capacity up to 77.16 pounds (35kg). Accommodates 440mm wide 3U or 4U chassis. Compatible with RM44, RM46, RM47, RM51, and RM52 chassis