Type Upright/Pendent/Sidewall/Concealed/ESFR Model ZSTZ ZSTX ZSTBS ZSTP ZSTDY ZSTY Nominal Diameter (mm): DN15 DN20 Connecting Threaded (Inch): 1/2" 3/4" Flux Coefficient: 80 115 Bulb Diameter: 5mm glass bulb for standard response 3mm glass bulb for quick response Response Time: 15seconds in general for 5mm glass bulb 8seconds in general for 3mm glass bulb Response Time Index RTI (ms)0.5: 87 for 5mm glass bulb 2225 for 3mm glass bulb