STN-2.5 is a stainless steel sampling tube. It's designed for use with the SL-2000 line of hardwired duct smoke detectors. This AC-P sampling tube measures 2.5' long and works with ductwork between 6" and 30" wide at the sampling point. • Designed to work with SL-2000N Duct-Mounted Smoke Detector • Fits in ducts less than 30" wide • includes 1 STN Sampling Tube for 30" Ducts and 1 Instruction Manual • Interconnection Capability: SL and RT Series • No Hazardous Material • No EPA Certification Required