Fastener Guide#

If you want your robot to stay in one piece, you will need fasteners. Fasteners are any pieces of hardware that mechanically join parts. This guide will discuss common types of fasteners, and how to use them on your robot.

Threaded Fasteners#

Bolts, screws and nuts are all threaded fasteners – meaning they use a helical thread to join parts.

Thread Basics#

To understand threaded fasteners, you will need to know some basic terminology

Diagram displaying thread pitch and the difference between internal/external threads and major/minor diameters.
External Thread

A thread on an outside surface. For example, bolts have external threads.

Internal Thread

A thread on an inside surface. For example, nuts have internal threads.

Thread Pitch

The distance from one thread to another, measured along the length of the thread. This can also be expressed as the number of threads per unit of length, for example threads per inch.

Major Diameter

The largest diameter of the thread profile.

Minor Diameter

The smallest diameter of the thread profile.

Thread Standards and Naming#

There are two main systems of naming and sizing threads that you will encounter in FTC: UTS imperial sizing and ISO metric sizing.

Imperial (UTS)#

The universal thread standard (UTS) is based on the imperial system and commonly used to size threads in the US and Canada. A UTS thread is named by a number indicating the major diameter of the thread, followed by the thread’s pitch measured in threads per inch.

For major diameters of ¼” or greater, first number is simply the major diameter in inches. For those smaller than ¼”, the following code is used:

no.

Major Diameter (inches)

#0

0.0600

#1

0.0730

#2

0.0860

#3

0.0990

#4

0.1120

#5

0.1250

#6

0.1380

#8

0.1640

#10

0.1900

#12

0.2160

Some common imperial thread sizes in FTC include ¼-20 (one quarter inch major diameter, 20 threads per inch) and #6-32 (0.138 inch major diameter, 32 threads per inch)

Metric (ISO)#

The ISO metric thread standard is commonly used worldwide, and for many products sold by FTC vendors.

A metric thread is designated by the letter M followed by the outer diameter in millimeters, for example M4 for a 4 mm major diameter bolt. This is then followed by a “x” and the pitch, also in millimeters. For example, “M4X0.7” means a M4 thread with a 0.7 mm pitch.

Bolts#

Bolts are the most commonly used fastener in FTC.

There are several types of bolts you may encounter, such as:

Socket Head Bolts

picture of a socket head bolt

These bolts have a cylindrical head and are tightened and loosened with a hexagonal recess.

Button Head Bolts

picture of a button head bolt

These bolts have a domed head, in contrast to the flat top of a standard socket bolt.

Grub Screws

picture of a grub screw

These bolts have no head, the recess is instead embedded within the threads. They are primarily used as set screws.

Hex Bolts

picture of a hex head bolt

The bolts are tightened with an external hex-shaped head. When designing for these bolts, it is important to allow clearance on the side of the head for tightening.

Every bolt requires a “drive” – meaning the geometry which is used to turn and install it. Each of the bolts listed above can have a variety of different types of drives:

diagram showing thread terminology

Nuts#

A nut is a fastener with an internally threaded hole. Together with a bolt, they’re used to join parts together.

Here are some types of nuts you may encounter in FTC:

Hex Nuts

picture of a hex nut

These most common type of nut. They can be tightened with a socket hex wrench.

Square Nuts

picture of a square nut

These are four-sided nuts. They work well in small spaces and can be easily inset into square pockets to keep from rotating.

T-slot Nuts

picture of a T-slot nut

These can be inserted into t-slot extrusion to tighten parts onto it.

Wing Nuts

picture of a wing nut

These nuts can be easily tightened without a wrench.

Nyloc Nuts

picture of a nyloc nut

These nuts contain a nylon ring which prevents loosening by increasing friction on the bolt thread. We recommend using these wherever possible.

Making Threads#

Sometimes, you will want to create new threads. This process is called threading. To create internal threads, you can use a cutting tool called a tap – essentially a sharper version of a screw.

To create external threads, you use a tool called a die.

diagram showing a tap and die

Threadlocker#

Bolts on your robot may loosen over time, especially if there are heavy vibrations. To prevent this you may use locking nuts or lock washers, which mechanically press against the thread. Another solution is to use a threadlocker, which is an adhesive compound that – as it’s name suggests – locks threads in place.

Loctite#

The most popular threadlocker among FTC teams is loctite. There are two types of Loctite: blue, which is removable, and red, which is permanent (and we mean it). To use loctite, apply it to the thread of the bolts.

Note

It is highly recommended that teams use Loctite on all motor and servo mounts, as well as any mechanism prone to vibration.

Danger

THE BOTTLE COLOR AND THE FLUID COLOR ARE REVERSED. When we refer to the “color”, we mean the fluid color. Blue loctite usually comes in a red bottle.

A red bottle containing blue (removable) loctite, and a blue bottle containing red (permament) loctite

Blue Loctite (removable, in red tube), Red Loctite (permament, in blue tube)#