The NS4 base is an electronics free 4" base featuring a plastic tamper-lock lug. Each base is equipped with a resistor. Models HSC-224R, HSC-220R and the HSC-221R are designed specifically for use with the Hochiki conventional models SLR-24H, SLR-24V, SLV-24, SLV-24N, SLV-24V, SLR-835, SLR-835H, DCD-135/190. The HSC-(X)R series is a 6" base with two sets of Form "C" relay contacts. Models HSC-224R, HSC-220R and the HSC-221R are also approved for use with Hochiki’s previous conventional model DFE 135/190.