ITWLinx's towerMAX DS-25 protects up to 25 2-wire or up to 12 4-wire digital stations lines using RJ-21X (Amphenol) connectors. The modules can be attached to expand system protection as your system grows. Other notable characteristics include Telco circuit protection, Signal Perfect circuitry, auto-resetting PTCs and metallic and longitudinal suppression modes. These equipments are ideal for the protection of telephone systems and fax machines.