Tradco Victorian Door Lever Handle on Long Backplate 0783 Bitkey is a type of Knob on a backplate consists of a lever with a keyhole cut just below it. Bitkey Function - allows a key to be inserted into the door to control a mortice sash lock. Just the like the lever latch, the door can be opened and shut by knob, but it can also be locked with a key. Made from solid brass. Specifications: Height: 152mm Width: 42mm Projection: 59mm Material: Brass Lock Type: Bitkey Screws: Included Finish: Antique Brass With this listing, by answering a couple of short questions, you can create a kit customised to your needs: For "Passage" doors (e.g. a bedroom that doesn't need locking), you will generally need a lever/knob + a Tube Latch. If it's a double door, you may also require flush Bolts. Flush Bolts are used to secure Double Doors, You can choose non-lockable and key-lockable option in various lengths. Alternatively, some customer's use a magnetic catch (such a PLS24PRO Magnetic Catch). For "Privacy" doors(e.g. a bathroom, en suite or a bedroom that you want to lock from the inside by turning a snib) you will generally need a tube latch as well a privacy bolt. For "Entrance" doors(e.g. a front / back door or any door that you want to lock with a key) you will generally need: A Mortice lock (if you have a rebated (slightly overlapping) double door, please choose a "rebated" version (which also comes with a rebate kit) Once you've determined the thickness of your door, you can select either a "Key/Key" (lock and unlock with a key from both sides) or a "Key/Thumb" (meaning you can lock the door from the inside using thumb turn, instead of a key). The choice here is one of personal preference. Flush Bolts For double doors, you will also need flush bolts. Flush Bolts are used to secure Double Doors, You can choose non-lockable and key-lockable options in various lengths. This is because the ball bearing reduces friction on the hinge and stops squeaking and wearing of the hinge Fixed Pin - Mainly used on internal doors. They can also be used on entrance doors that are not heavy Loose Pin - Internal use only. Mostly used on bathroom door so the door can be removed (lifted off) in the locked position (e.g. in case of an emergency) Depending on the weight of your door, you will generally need 3 hinges for an Entrance door (which are more solid) and 2 hinges for internal doors. Please use the tables below as a guide on the number of hinges you require, as well as the recommended hinge positioning.