An adjustment screw is a screw which is used to make very small and precise adjustments. A variety of objects from embroidery hoops to heavy machinery are fitted with adjustment screws which are designed to be used to ensure that something works at an optimum level. Because adjustment screws represent a potential point of weakness as a moving part, they may be specially reinforced to stabilize the object they are adjusting, and it is usually possible to obtain replacements in event that a screw is damaged in some way.
With an adjustment screw, it is possible to carefully adjust things like spacing and tension. For example, on a pair of locking pliers, the adjustment screw is used to space the head of the pliers to the desired width so that when the pliers are close, they will lock in place at that width. On something like an embroidery hoop, the screw is used to loosen the hoop to insert fabric, and to tighten it back up again to restore tension and hold the fabric in place.
Adjustment screws are found on many types of heavy machinery to allow people to make precise adjustments as needed. Printing presses, for example, can use adjustment screws to adjust the level of the print bed for various needs, or to adjust the distance between the rollers on the press. The purpose of such screws is to allow people to make small compensations for natural variations and the wear which occurs over time.
Some adjustment screws are designed to lock, so that once they are adjusted, they will hold their positions. This may be done with an attachment which must be loosened to move the screw, or with a carefully engineered design which prevents the screw from moving unless someone uses a tool such as a screwdriver to move in. Locking maintains safety and reliability by confirming that the setting of the adjustment screw will remain the same until someone actively decides to change it.
On objects and equipment with adjustment screws, the screw and its function are usually discussed in the manual. It's important to read about how and when the screw should be adjusted. Failure to adjust the screw when needed can result in damage or make some tasks much more difficult than they need to be. The adjustment screw also needs to be kept clean and oiled so that it will move smoothly, as rough movement can interfere with very minute adjustments.