Screws Nuts and Bolts

Fasteners

Overview

Machine screws, bolts, and nuts are essential fasteners used in mechanical assemblies to hold components together. They come in various types, each designed for specific applications. Below is an overview of common types and uses of Screws Bolts and Nuts in Robotics.

Machine Screws

Machine screws are threaded fasteners typically used with nuts or threaded holes. They are smaller in size compared to bolts and are often used in precision work.

Flat Head Machine Screw
- Description: Flat top, countersunk design.
- Use: For applications requiring a flush surface, such as electrical devices or metal assemblies.
Round Head Machine Screw
- Description: Rounded top with a flat underside.
- Use: Provides a decorative finish, often used in light-duty applications.
Pan Head Machine Screw
- Description: Rounded top with a large flat bearing surface.
- Use: Securely holds thin materials like sheet metal or plastic.
Phillips or Slotted Drive Machine Screws
- Description: Head designed for Phillips or flathead screwdrivers.
- Use: Common in general assembly and repair.
Hex Head Machine Screw
- Description: Hexagonal head for use with a wrench or socket.
- Use: Offers greater torque for tightening.
Socket Head Machine Screw
- Description: Cylindrical head with an internal hex drive.
- Use: Used in applications requiring high strength and a clean appearance.

Most Common Head Types

Socket

Socket heads are often used for high-strength fastening in machine tools, dies, and fixtures. With a deeper drive than rounded and flat head screws, they transmit more torque as they're fastened for a tighter hold.

Socket heads are narrower than hex heads, so they're good for tight spaces since you don't need clearance for a crescent wrench. Keep in mind that the shorter the head is, the weaker it is—so low-profile socket heads shouldn't be used for high-strength applications.

These heads sometimes have knurls, which adds grip for initial tightening by hand.

Flat

Flat heads fit in countersunk holes or sink down into your material for a flush finish. This leaves a clean, smooth look while preventing the head from snagging any surrounding parts. However, the V-shaped head has less holding power than other common head types, so flat head screws shouldn’t be used for any load-bearing or high-strength fastening.

Headless (Set Screws)

Headless fasteners, usually set screws, install flush into your equipment for a discreet look. Set screws are often used to hold sleeves, collars, gears, and other parts in place while remaining largely out of sight.

In addition, some shoulder screws are headless, enabling them to be used as pins or dowels to align components.

Rounded or Pan Head

Rounded heads are one of the most common fastener head types. They have a large bearing surface that can span wide holes. The domed top has a decorative look and comes in a variety of styles, including pan, button, and truss.

Hex Head

Hex heads are often used for high-strength fastening. As they're tightened, they transmit more torque for a tighter hold than square heads, but not as much as 12-point heads.

Tighten with a wrench or 6-point hex socket. You can also use a 12-point socket, which aligns quicker but won't grip as well.

Nuts

Machine nuts are threaded fasteners used in conjunction with machine screws or bolts to securely hold components together. They come in various shapes, sizes, and types, each designed for specific applications and environments. Understanding the different types of machine nuts and their applications is crucial for selecting the right fastener for a specific engineering or construction task. Here are the different types, what they look like and what they are used for.

Materials

Steel: Durable and affordable; can be coated for corrosion resistance.
Stainless Steel: Highly resistant to corrosion.
Brass: Corrosion-resistant and decorative.
Plastic (Nylon): Lightweight, non-conductive, and resistant to chemicals.

Applications

Mechanical Assemblies: Pair with bolts or screws for secure joins.
Vibrating Environments: Use lock nuts to prevent loosening.
Aesthetics: Cap nuts for decorative purposes.
Woodworking: T-nuts for embedding in wooden components.

FRC Most Common Fasteners

We use many different types of fasteners in FRC, but here are the primary Screws, Bolts and Nuts that we use.

3/8-16 - Most often used for Drive system Axles (particularly on Tank Drive systems. Make sure these are Hex Head Grade 5 or Grade 8 Steel so they do not Bend
1/4 - 20 - Common for mounting and bracing applications where significant weight or force will be applied. Climbers, Winches etc. We also used these regularly with 1" T-Slot systems.
10-32 - This is the most common screw we use. It fits through the holes in the Rev Extrusion and is the size used for munting the planetary gear boxes. Nut size is 3/8" and the Allen Keys are Red Tape (5/32) for Socket heads and Green Tape (1/8") for Pan Heads. Be careful not to mix with 10-24 as they have the same diameter but will cross thread the hole and ruin your day.
8-32 - Used regularly for component/COTS assemblies include SDS Modules etc. Nuts are 11/32" White Tape Wrenches and the Allen Keys are Blue Tape (9/64") for Socket Head and White Tape (3/32") for Pan Head.
6-32 - Less common on the robot but used on occasion within mechanisms.
4-40 - Common uses include mounting electronics, PCBs and Sensors.
2-56 - Mounting small electrical sensors and the Anderson connectors.

Other Notes:

Material: Stainless Steel (18-8 or 316), Black Oxide, Zinc Plated
Drive Type - almost always Hex (allen key) drive or Hex for a wrench.
Head Type - Mostly Pan Head and Socket Head. Flat head for countersunk holes are used as well.
Nuts are almost always Nylock to prevent loosening.