A marking knife is a woodworking

Woodworking

Woodworking is the process of building, making or carving something using wood.-History:Along with stone, mud, and animal parts, wood was one of the first materials worked by early humans. Microwear analysis of the Mousterian stone tools used by the Neanderthals show that many were used to work wood...

 layout tool. It is used to scribe a line to be followed by a hand saw

Hand saw

In woodworking and carpentry, hand saws, also known as "panel saws", "fish saws", are used to cut pieces of wood into different shapes. This is usually done in order to join the pieces together and create a wooden object. They usually operate by having a series of sharp points of some substance...

 or chisel

Chisel

A chisel is a tool with a characteristically shaped cutting edge of blade on its end, for carving or cutting a hard material such as wood, stone, or metal. The handle and blade of some types of chisel are made of metal or wood with a sharp edge in it.In use, the chisel is forced into the material...

 when making woodworking joints

Woodworking joints

Joinery is a part of woodworking that involves joining together pieces of wood, to create furniture, structures, toys, and other items. Some wood joints employ fasteners, bindings, or adhesives, while others use only wood elements. The characteristics of wooden joints - strength, flexibility,...

 and other operations.

Marking knives have a steel blade which is sharpened to a knife edge. The purpose of the knife edge is to sever fibres as the marking knife is drawn over them. This produces a very accurate line which aids in making accurate cuts with the saw or chisel. The blade is of tool steel with a hardwood or plastic handle.

These instruments

Measuring instrument

In the physical sciences, quality assurance, and engineering, measurement is the activity of obtaining and comparing physical quantities of real-world objects and events. Established standard objects and events are used as units, and the process of measurement gives a number relating the item...

 are generally used when laying out across the grain. They are avoided when laying out with the grain as the blade tends to follow the fibres, resulting in inaccurate lines. The scratch awl

Scratch awl

A scratch awl is a woodworking layout and point-making tool. It is used to scribe a line to be followed by a hand saw or chisel when making woodworking joints and other operations....

 is preferred for long grain

Wood grain

In speaking of wood the term grain refers to the alternating regions of relatively darker and lighter wood resulting from the differing growth parameters occurring in different seasons . The term is used in several ways. Perhaps most important is that in woodworking techniques...

layout.