The Right Wrench For Your Grub Screw

Grub screws, also known as set screws, are a type of fixing screw used to join one component or part securely to another. They are designed to offer a secure grip without the use of a nut, despite functioning similarly to a bolt. Unlike bolts, grub screws are fully threaded and driven into an existing tapped hole, and they lack a protruding head, instead featuring a sunken internal recess at the head end. The internal-wrenching drive used to seat a headless grub screw can be a hex socket, a star (Torx) socket, a square socket, or a regular slotted drive. The size of the grub screw and corresponding wrench are important considerations, with sizes typically ranging from a couple of millimetres to several millimetres or inches in length and diameter.

Grub screw sizes in metric and imperial units

Grub screws, also known as set screws, are a type of fixing screw that is used to join one component or part securely to another. They are designed without a protruding head, allowing them to be driven fully into pre-drilled holes. The lack of a head also means that the entire length of the shaft can be threaded, maximising thread engagement.

Grub Screw Sizes in Metric Units

Metric grub screws are available in diameters ranging from M1.2 to M16, and lengths from 1.50mm to 190.00mm. The sizes are typically given in the format 'MxL', where 'M' refers to the major (outer) diameter of the thread in millimetres, and 'L' is the length in millimetres. For example, an M8 x 12mm grub screw has a diameter of 8mm and a length of 12mm. Common sizes for metric grub screws include:

• M1
• M2
• M3
• M4
• M5
• M6
• M8
• M10
• M12
• M14
• M16
• M20

Grub Screw Sizes in Imperial Units

Imperial grub screws are manufactured in a range of diameters, from No. 0 to 3/4 inch, and lengths from 1/16 inch to 4 inches. The sizes are given in either inches or fractions of inches.

Hex key wrenches for grub screws

Hex key wrenches are a type of simple driver for bolts or screws with heads that have internal hexagonal recesses (sockets). They are formed from a single piece of hard hexagonal steel rod, bent to 90 degrees, forming two arms of unequal length that resemble an "L". The most common type of drive style for grub screws is the hex head, which can be either an internal recessed drive socket (as in a true grub screw) or a protruding head on a set screw. Hex keys are designated with a socket size and are manufactured with tight tolerances, so they are commonly sold in kits with a variety of sizes.

When it comes to using hex key wrenches for grub screws, it's important to know the correct Allen key sizes, which can usually be found on the packaging. The internal-wrenching drive used to seat a headless grub screw can be a hex socket (Allen key), a star (Torx) socket, a square socket (Robertson drive), or a regular slotted drive. The correct type of drive will depend on the brand, model, and exact type of screw being used.

Grub screws are typically used to join or clamp one object or component tightly against another, especially in situations where a standard nut and bolt would impede the optimal functioning of an object or component. They are commonly found in mechanical systems where two or more metal surfaces rub or press directly together, and there isn't room for a bolt or protruding head.

When using hex key wrenches for grub screws, it's important to note that slotted varieties are less common than hex, Torx, or Allen internal-wrenching drives. This is because slotted varieties are less robust and more easily deformed during insertion under high torque forces. Hex keys provide a secure, non-slip, and deformation-resistant drive socket for seating grub and set screws with high torque forces.

Some common sizes for hex key wrenches include metric sizes defined in ISO 2936:2014, such as 0.7 mm, 0.9 mm, 1.3 mm, 1.5 to 5 mm in 0.5 mm increments, and 5 mm to 19 mm in 1 mm increments. There are also US customary hex key sizes defined in ANSI/ASME standard B18.3-1998.

Flat-end grub screws

One example of a flat-end grub screw is the M6 x 10mm screw from Unbrako, which is made from stainless steel and is suitable for use with Allen key products. Another example is the Pinnacle M5-M8 Black Assorted Grub Screw Set, which includes both hex head and socket set screws. This set provides a range of options for securing objects and can be tightened using a wrench or hex screwdriver.

Cup point grub screws

The cup point grub screw features a hex drive at one end and a cup-shaped indentation at the other. The thin edge of the cup end digs into the contact surface, providing high holding power. This makes it suitable for permanent and semi-permanent placements, although it will leave some indentation on the surface.

Grub screw kits

Grub screws, also known as set screws or blind screws, are used to join objects together. They are fully threaded and do not have protruding heads, which means they can be fully driven into a hole without the need for a countersink. They are typically used in applications where exposed parts of bolts and nuts would interfere with the operation of devices. Grub screws are usually made from stainless steel or high-grade alloy steel and come in different diameter sizes and lengths.

There are a variety of grub screw kits available, ranging from 12-piece kits to larger kits containing 410 pieces. The kits usually include an assortment of metric grub screws, with sizes ranging from M3 to M8. Some kits also offer imperial measurements, with sizes from 5/32" to 3/8". It's important to select a kit that includes the sizes and measurements suitable for your specific needs.

In addition to the screw assortment, some kits also provide Allen keys or other tools to suit your grub screws. For example, the 75-piece kit from Robson's Tool King Store offers a range of popular-sized grub screws, while the 410-piece kit from eBay provides a comprehensive set of stainless steel metric grub screws with a range of sizes.

Frequently asked questions