There are two main types of light bulb cap: Edison screw (ES) and bayonet (BC). The most common sizes are: Hooked, where the lamp holder has a hook for suspending using chain, rope or hooking over a fixture. Hooked lamp holders should still have a cord grip - the chain secures the lamp holder, but there needs to be a device for stopping the supply cable being pulled out. Cord grip, where the lamp holder includes a cord grip to secure the supply cord and is is suspended as a pendant light. Common types include a compression fitting, looping the cable round an internal obstacle, or a screw which presses against the cable Threaded, where the lamp holder has a threaded component which is used to mount it on a support. Common in table/standard lights where the lamp holder is fixed to the base/stem of the lamp, and also used in conduit applications. These used to be called 'nipple' lamp holders. The threaded parts come in a range of metric and imperial sizes.