A Complete Guide to Thumb Screws

This expert buyer’s guide will give you all the basic information you need when choosing and buying thumb screws for a wide range of jobs. In addition to explaining exactly what thumb screws are, we will discuss their many uses, and outline the various features, materials, and sizes of thumb screws available to buy online.

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.

Thumb screws and thumb screw bolts can also be useful solutions in a situation where you may need to remove a component or panel regularly. They can make tasks such as maintenance or cleaning much quicker and easier than having to use a driver to remove fully torqued machine screws, bolts, or rivets.

Various sorts of fasteners and fixings might fall under the broad thumb screws definition. A true thumb screw or bolt can be distinguished from standard bolts or rivets by its large head, offering easier grip. They will often have knurled edges around the head section too, further improving friction and purchase while being turned by hand. They may or may not feature a slot in the head for a screwdriver to be used if preferred. Washers are not normally needed with this type of fastener.

Knurled Thumb Screws

Knurled thumb screws are commonly chosen because they give the user a better grip on the head of the fastener when installing by hand.

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.

Knurled head thumb screws are one of the most common applications of this technique, which can be found on many types of stainless steel or nylon nuts, screws and bolts. The pattern of bumps, ridges or notches allows for much-improved friction between fingers and the otherwise smooth edges of the thumb screw.

Thumb Screw Knobs

Thumb screw knobs, often referred to simply as thumb knobs, are closely related to thumb screws. However, they are specifically designed to be used as quick, easily removable fastener solutions for tightening something down and releasing it on demand.

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.

The head section on a thumb screw knob will often be made of plastic (nylon) or resin (Yuliya resin thumb screws are common) and manufactured as a separate piece to the metal threaded section of the screw-in shaft itself. Indeed, nylon knurled head knobs can often be bought on their own, with the heads intended to be press-fit onto thumb screws for easier installation and removal.

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.

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.

Having a thumb knob rather than a traditional slotted screw for designs like this is an easy way to save a lot of time and hassle during regular opening or closing. Thumb screws are ideal for applications where you just need something light, easy, and quick to work.

Thumb screws are best used in applications where the fastener doesn't need to be torqued excessively tightly.

Due to the hand-driven nature of these fixings - especially ones that do not feature a slotted head - they are often inherently limited in terms of the overall tightness you can realistically achieve. Thumb bolts or knobs are also broadly unsuitable for high vibration applications, where they may be at risk of loosening over time.

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.

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.

The length of a thumb screw is almost always stated in millimetres (mm) and measured from just below the heads or shoulders to the opposite (flat) end of the threaded section.

Metric Threads

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.

The metric sizing (M5, M6, M12 etc) is a reference to the diameter of the shaft in mm, while thread measurements are taken from ridge to ridge on the threaded shaft section itself. An M4 brass thumb screw, thumb bolt or thumb knob with a stated thread size of 0.75mm will therefore be 4mm in core shaft diameter, with a 0.75mm gap between each of its threads.