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Freshly Baked Science

keys lying out on yellow background held together with a keyring black and white with colour

Under Lock and Key

20th October 2018

You’re almost guaranteed to use a key at least four times a day… locking and unlocking your house and car, starting your car, locking up your bike, opening and closing windows and lockers… even locking up your diary! But how do these devices actually work?


Most locks consist of two parts. One part is static (doesn’t move), for example, on a door, it is the part attached to the door frame. This is usually a metal component, used to reinforce a hole in the door frame, making it sturdier and harder to break open. The other part of the lock is the part which fits into the hole in the door frame. This consists of a mechanism which moves a large bolt in or out of the hole (it is locked and out is unlocked). In order to slide the bolt across, you need a mechanism that can turn rotary motion (turning a key) into reciprocating motion (sliding of the bolt). All locks have to have a slightly different internal mechanism so that only one key shape can open that specific lock.


A common type of lock is the ‘pin tumbler lock’, which is mostly seen on front doors. Inside the lock, there are a series of pins lined up, with springs on top of them. These pins are split into two, with the top half resting on the bottom. The top pin is called the ‘driver pin’ and the bottom pin is called the ‘plug’. When a key isn’t in the hole, the plugs will all rest at different heights. In order to be able to turn the key, all the plugs must be at the same height. When the correct key is inserted into the lock, the grooves on the key correspond to each plug, pushing them all to become the same height as each other, allowing the lock to be turned. If the wrong key is inserted, the plugs will remain at the wrong height and won’t be able to turn.


Is it true that there are keys which can open more than one lock?


If you’ve ever lost or forgotten your locker key, you will know that someone in the school has a ‘master key’. This is a key that can be used to open more than one lock! Master keys can only be used on locks that have been designed to be opened by two keys. A master lock will have a third pin in it, which sits in between the driver pin and the plug. This pin is called the ‘spacer’. With the addition of a spacer, there are now two ways that the lock can be opened. One is with a normal key, designed exactly for that specific lock and the other is with a master key. The master key will push the spacers into alignment, allowing the key to turn!


If you’d like to know more about different types of keys and locks, for example, electronic locks on cars, then let us know via social media (@wonkscience) or email (hannah@wonkmagazine.co.uk) and we will get another article published for you!

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