Wrenches

The five most common types of wrenches are:

Adjustable Wrench 

Combination Wrench

Ratcheting Wrench

Crowfoot Wrench

Flare Wrench

A Wrench is a hand tool used for tightening and loosening nuts/bolts, typically with a fixed size and shape in areas where a typical ratchet and socket can not fit. It may have an open-end or box-end design, and may be adjustable or non-adjustable.

A Socket Wrench or Ratchet is a type of hand tool that allows for continuous rotation of the fastener in only one direction without ever having to disengage from the fastener. It is typically used with a set of interchangeable socket attachments, allowing for a wide range of sizes and shapes to be turned with the same tool.

A Combination Wrench is a type of hand tool that has two different ends. One end has an open jaw for tigheting and loosening nuts/bolts in constricted areas or applications where a box end will not fit. The other end has a closed, ring-shaped jaw (also called a box-end) that completely fits around the fastener to prevent slipage and for added torque. 

Overall, the open-end side is useful for quickly tightening or loosening fasteners, while the closed-end side is ideal for high-torque applications where extra force is needed.

Combination Wrenches are typically made of steel and come in a range of sizes.

There are a variety of different types of finishes that can be found on wrenches, including:

Polished: This finish is shiny and reflective making it easy to clean while being rust and corrosion resistant.

Matte: This finish is less reflective than a polished finish, and is often used on tools that are exposed to harsh environments. It helps to hide scratches and wear, and is less likely to show fingerprints.

Black Oxide: This finish is a dark, matte/satin black color and is often used on tools that are designed for heavy-duty use. It helps to prevent rust and corrosion, and can also reduce glare.

Overall, the finish on a wrench is primarily a matter of personal preference and the intended use of the tool. 

SAE (Society of Automotive Engineers) and Metric are two different systems of measurement used to indicate the size of nuts, bolts, and other fasteners.

The SAE system uses inches as its base unit of measurement. In this system, the size of a fastener is expressed in fractions of an inch. For example, a 1/2-inch wrench is used to turn a nut or bolt that measures 1/2 inch in diameter.

The Metric system, on the other hand, uses millimeters as its base unit of measurement. In this system, the size of a fastener is expressed in millimeters. For example, a 10mm wrench is used to turn a nut or bolt that measures 10mm in diameter.

The primary difference between SAE and Metric is the unit of measurement used to express the size of the fastener. While SAE is more commonly used in the United States, Metric is used in most other countries around the world. It's important to use the correct type of wrench or socket for the fastener being worked on to prevent damage or injury.