Pendent sprinkler: hangs below ceiling (most common type). Activation: 155F ordinary temperature rating fusible link or glass bulb. Coverage: standard spray 15x15 ft max (225 sf) per NFPA 13 Table 8.6.2.2.1. K-factor: 5.6 (standard), 8.0 (large orifice for high-challenge). Thread: 1/2in or 3/4in NPT. Deflector: below ceiling plane — distributes water in umbrella pattern. Concealed type: flat cover plate (activates before sprinkler, drops to expose head). Quick-response: 3mm glass bulb (vs 5mm standard) — required in light hazard, residential. ESR: early suppression fast response — high-challenge storage. Temperature ratings: ordinary 135-170F, intermediate 175-225F (near heat sources), high 250-300F. Install within 1in of ceiling (max 18in per NFPA 13). Escutcheon covers ceiling plate. Cost: $5-$25 each. CSI 21 13 13.