NO means that the circuit is open when below the item marked temperature, when above the item marked temperature, the circuit is closed. Automatic reset. NC means that the circuit is closed when below the item marked temperature, when above the item marked temperature, the circuit is open. Automatic reset. 10A 250VAC Circuit resistance: 50 Mohm Insulation resistance: 100 Mohm Withstand voltage: 1500V AC/minute Opening-closing durability: 10000 times or more (under rated load) Type:Optional Temperature: Optional Dimensions: As shown in the picture. Qty: Optional