Screw captivation is important because in the past, screws were going missing during machine maintenance, leading to panels being improperly reattached after servicing, eventually resulting in workplace injuries when people accidentally put their hands inside machinery. For this reason, permanent fastenings (such as captive screws) are now legally required on certain equipment, such as safety covers/panels, to comply with EU law (2006/42/EC; Machine Safety Directive) and/or ISO 14583. The use of captive screws minimises the chances of a screw being lost during servicing or maintenance because usually, the captive screw remains with an assembly - e.g. a guard panel that can be lifted off another part. In the same way, wing nuts and screws and knurled nuts and thumb screws also provide a far greater grip (and hence torque) than a plain nut, and are designed to be tightened by hand, although the metal variations can be tightened or loosened using tools if necessary. This extra grip also makes them easily removable when needed. Thrust pads can be used in combination with screws to prevent marking, scratches or dents to materials that are easily damaged. Generally, captive screws have a smooth (non-threaded) shoulder/shank that has a smaller diameter than the threaded end portion. The captive screw is placed through the first panel and then on to the frame (e.g. machinery housing). The captive screw is placed through the first panel either: via a threaded hole in the panel, or - if the panel is non-threaded - via a threaded washer or retaining flange.

Thumb screw thread gauge and diameter are typically stated in metric units in the UK. Elsewhere, measurements given in inch sizes may be more widespread. Common sizes that fit the threaded holes in a wide variety of everyday UK devices, panels and covers include M6 thumb screws, M4 knurled thumb screws, M8 thumb screws, and M12 thumb screws. Most thumb screws come in either long or very short lengths, depending on the application where they are needed. To choose the best thumb screw for the task, it is important to bear in mind certain characteristics such as length, diameter, and thread size.Thumb screws (sometimes written as thumbscrews) are multipurpose fasteners designed to be tightened and loosened by hand, rather than needing tools like screwdrivers or wrenches for installation. They have a wide range of useful applications, especially in parts, materials and builds that do not easily support the use of manual or power tools. This is often due to space restrictions. Knurled bolts and screws of this type are so-called because of the knurling pattern - a series of machined ridges or bumps - found around the screw head. Knurling is a widespread manufacturing technique for improving grip or torque force on a huge array of hand-installed components and fasteners. Examples of typical applications include instrument panels, case lids, battery compartments and enclosure windows. A thumb knob may also be listed as a star knob, depending on the precise shape of the head designed for gripping by hand. Thumb screws are best used in applications where the fastener doesn't need to be torqued excessively tightly.

Knurled Knobs, or Thumb Knobs easily press fit on to screws, creating a small knob for clamping or securing an application. These Thumb Screw Knobs, also known as Thumb Bolts, can be used with any length of screw. The knurled edge is easily gripped for tightening and loosening. Passivation is a process designed to remove foreign metals or impurities which may have been introduced during manufacturing/processing from the surface of stainless and corrosion resistant steels. This helps keep the protective anti-corrosion surface film intact and slows corrosion. Captive screws are designed to provide “captivation” (meaning a permanent hold). Captive screws can still be removed from their installation, but only intentionally - they are very unlikely to fall out accidentally once installed because the smooth shoulder of the captive screw remains in the panel unless specifically unscrewed. Knurled thumb screws are commonly chosen because they give the user a better grip on the head of the fastener when installing by hand.A second common scenario where thumb screws are often the best choice is where regular and repeated loosening or tightening of the fastener will be necessary. This is often the case for things like battery covers, enclosure doors and electrical safety panels. One of the main reasons why thumb screws are often chosen over traditional screws is that certain parts and assemblies do not leave much room for using hand tools. If a panel or component needs to be fastened down reasonably tightly, but access for a screwdriver or wrench is limited, manufacturers will often choose to include a thumb screw instead. Small thumb screws can be as short as 4mm or less from the shoulder to the end of the threading, while long thumb screws commonly extend to around 25-30mm (1 inch) and beyond. It is unusual to find very long thumb screws for most day-to-day fastening jobs. This tends to imply that the product would need to be more rigid (less range of deflection) and have greater tensile strength than most of these relatively small fasteners tend to offer. Yellow to orange colour depending on a proprietary process used. Will range from matt to bright finish depending on base metal. Good corrosion resistance and high tarnish resistance.