The yale 81 rollerbolt nightlatch front door lock has a rollerbolt for pushpull action making it ideal to prevent accidental lock out ideal for communal or flat entrance doors it is opened by a key from the outside and a turn handle operation from inside the 81 rollerbolt nightlatch has a 60mm backset this is the measurement from the edge of the door to the centre of the keyhole locks with a 40mm backset are normally used where there is restricted space such as on a narrow glass panelled door 10