Bicycle manufacturers typically use a variety of bolts in different sizes and types during the assembly process. Some common types of bolts used in bicycle manufacturing include:

Hex bolts: These are standard bolts with a hexagonal head and a threaded shaft. They are commonly used in various parts of a bike, such as the frame, handlebars, and stem.

Socket head bolts: These bolts have a cylindrical head with a hexagonal socket for a wrench or Allen key. They are often used in places where a low-profile bolt head is needed, such as on brake calipers.

Torx bolts: Torx bolts have a star-shaped head and are designed to provide better torque transfer and resist cam-out compared to traditional hex bolts. They are commonly found on disc brake rotors and some components.

Allen bolts: These bolts have a hexagonal socket in the head and are tightened or loosened using an Allen key (also known as a hex key). They are used in various parts of a bike, including the seat post, stem, and brake calipers.

Phillips head bolts: While less common in modern bikes, some older or certain components may still use Phillips head bolts. These bolts have a cross-shaped head and require a Phillips screwdriver for installation.

Flat head bolts: Flat head bolts have a countersunk head that sits flush with the surface when installed. They are used in places where a smooth finish is desired, such as on some accessory mounts.

The specific type and size of bolts used in bicycle manufacturing can vary depending on the components and materials being assembled. Manufacturers often choose bolts based on factors like strength, weight, corrosion resistance, and ease of maintenance.