Zero 350A Sill Protection Automatic Door Bottom with Solid Neoprene Insert – Mortised – Mill Finish AluminumSill Protection Automatic Door BottomMount: MortisedRegular DutyInsert: Solid NeopreneFinish: Mill Finish AluminumMaximum effective drop: 1″Fire RatedSupplied with #350 End CapsSupplied with solid neoprene extrusion, self-extinguishing, under MIL R6855 Type II Class 40 oil resistantRated for 5 million cyclesZEROs patented automatic door bottom technology ensures a tight seal against the floor or saddle. As the door is closed, an adjustable “plunger” is compressed against the door frame, activating a concealed flat spring mechanism. This mechanism drops the seal smoothly from the housing in a scissor-like motion as illustrated below. The door seal compresses tightly even on uneven surfaces and retracts automatically when the door is opened.All ZERO automatic door bottoms function the same way. The concealed spring mechanism causes the insert seal to activate on the hinge side first. It prevents the seal from dragging along the floor or threshold while the door is being closed to avoid door hang-up or closing delay.