A rubber O-ring on these plastic deck plates creates a watertight seal for safety. Screw-in style has a single-start, non-jamming (no cross-threading), extra-strong, self-cleaning buttress thread. Use only 100% silicone caulk. ShWt .4Material: UV-resistant ASA plastic (West Marine-manufactured models with eight-digit Model Numbers), ABS plastic (all others, which are manufactured by Beckson)Fasteners: #8 pan head screws or thru-bolts (sold separately)Warranty: One year