Check the listing for details. OC-55 Normally Closed Alarm Security Rolling Gate Magnetic Reed Switch. Color: Silver Gray, Condition: New. Listed at 15.61 USD. Description:1.Actuation Distance: 40-50mm. Zinc Alloy Housing, Stainless Steel Pipe.2.The reed switch is an electrical switch operated by an applied magnetic field.3.Designed for use with alarm systems. Great for use in family and factory window, door. etc.4.Screw Mounted for easily install.5.NC means Normally Closed:When the magnet together, the circuit is conductive( light on ); when the magnet separate, the circuit is not conductive ( light off ). When make order,pls check carefully!Specification:Product Name: Magnetic Door SwitchModel: OC-55Contact Type: NCActuation Distance: 40-50mmMax. Current: 0.5AMax. Power: 10WWorking Voltage: DC100VSize(Approx): 105 x 37 x 9.7mm, 105 x 15.7 x 15.3mm (L*W*H) Hole Dia.: 5.33mmCable Length(Each): 50cm / 19.7-inchPipe Thread Length: 26mm / 1.