When the particle beams enter the detectors, insertion magnets take over. Particles must be squeezed closer together before they enter a detector so that they collide with particles coming from the opposite direction. Three quadrupoles are used to create a system called an inner triplet. There are eight inner triplets, two of which are located at each of the four large LHC detectors, ALICE, ATLAS, CMS and LHCb. Inner triplets tighten the beam, making it 12.5 times narrower – from 0.2 millimetres down to 16 micrometres across.