Among the tools available to measure an angle, a protractor (or engineering protractor) is a simple mathematical and geometrical instrument used for drawing, measuring, and plotting angles.
Protractor has a scale that is graduated in angular unit degree, on its outer most circular edge and has a vertex mark right at its center of its base. Vertex mark is used as a reference point for measurement and from here one can measure different angles ranging from 0 to 360 degree.
Protractors are usually made from clear transparent plastic or glass but depending on the usage it can be made from steel and wood too. Depending on the system of measurement, a protractor can have a radian scale or degree scale on it.
In most common configuration protractor has a semi-circular shape that is divided into hundred and eighty parts or a full circular shape divided into three hundred and sixty parts.
The 8 Types of Protractor
There are many types of protractors available in the market with each have its own unique design, working, applications and advantages. Some of the most common types of protractors based on their design are as follow
- Semi-circle Protractor
- Full circle Protractor
- Quarter Circle Protractor
- Square Protractor
- Miter Protractor
- Medical Protractor
- Bevel Protractor
- Single-arm Bevel Protractor
- Double-arm bevel Protractor
- Vernier Bevel Protractor
- Optical Bevel Protractor
- Digital sliding T Bevel Protractor
- Digital Protractor
- Single-arm digital protractor
- Double arm digital protractor
1. Semi-Circle Protractor (Half-Circle)
Perhaps, the semi-circle protractor or half-circle protractor is the most common and most used type of protractor. It is mostly used in the education sector where students are taught the basics of geometry and how to find and draw angles.
In terms of its shape, it consists of a half-circle body with a vertex marked on its base center. It has scale graduation in degree on its outermost circular edge. A semi-circle protractor can measure an angle between 0 to 180° with a resolution of one degree.
Graduation is marked in such a way you can measure an angle from any side meaning from left to right and vice versa from right to left. You can use it to draw, measure, and plot different angles. For angle measurement, its most application is for the angles in a drawing (2 dimension object).
Advantages of semi-circle protractor:
- Semi-circle protractor as a very simple design
- It is easy to understand
- Easy to operate
- It’s easy to read
- Semi-circle protractors are easily available on the market
- Relatively little maintenance
- They are low-cost tools.
2. Full Circle Protractor
Full circle protractor is not a commonly used tool and it’s rarely used for education purposes. It’s mostly used by engineers, meteorologists, and architects to mark angles on products for manufacturing and making architectural drawings of buildings and other structures.
It consists of a full circular body with a vortex at the center of the body. A full circle protractor has scale graduation in degree on its outermost circular edge. It can measure angles between zeros to three hundred and sixty degrees with the precision of one degree.
Graduation is marked in such a way that the reading increased from zero to 360 degrees in a clockwise direction from an astronomical north reference point. It can be sued to draw, measure, and plot different angles.
Advantages of semi-circle protractor:
- Moderately easy to understand
- Easy to operate
- Moderately easy to read
3. Quarter Circle Protractor
A quarter-circle protractor is not a common tool and it’s mostly used for professional works like making manufacturing or architecture drawings.
It’s mostly used by engineers, meteorologists, and architects to mark angles on products for manufacturing and making architectural drawings of buildings and other structures.
A quarter-circle protractor consists of a quarter of a circular body with two of its side edges shaping a 90-degree corner. A single quarter-circle protractor can have the number of scale graduation on it with each scale having a different unit.
Advantages of quarter circle protractor:
- The quarter-circle protractor has the ability to effectively mark angles on workpieces that has limited space with right angle between its two sides.
4. Square Protractor
As its name says it’s a square shape protractor and it’s also known as the military protractor as it’s mostly used by military personnel for finding the location of enemy or friendly troops on their maps. It is very helpful in finding the grid azimuth from given points on the map.
This protractor has two scales graduated on it. One is the inner scale that is marked from zero to three hundred and sixty degree and second is the outer scale that is graduated in millimeters. As per the rules, the 0° or the 360° of the square protractor should be toward the north of the map.
The center of the square protractor is at the intersection of the vertical hundred and eighty degrees line and horizontal line. The baseline of the square protractor should be aligned apparel to the north-south grid line of the map.
Advantages of the square protractor:
- perfect and precise tool to measure land on maps
- can predict travel routs perfectly
- able to draw perfect grid lines on maps
5. Miter Protractor
Miter protractor is a dedicated angle measuring device that is used to measure or draw angles within a confined space. It is mostly used by the professionals like plumbers, wood workshops, and metal workshop workers.
Miter protractor consists of a circular disk-like body that has two long legs attached to it. The circular disk has scale with graduation marks in different units on its outer edge. Both arms of the miter protractor can move independently to 360 degrees.
The scale of the miter protractor has graduation for a miter cut scale and a single cut scale. During operation when legs of the protractor are adjusted for measurement, the protractor provides the angle for the miter, single and compound cuts.
Advantages of miter protractor:
- Miter protractor can measure angle for different cut setting
- It’s quite easy to operate a miter protractor all you need is to adjust the legs as per the requirements
- Miter protractor gives an accurate reading each and every time as long as the protractor is in good condition
6. Medical Protractor
Medical protractor is specifically designed for the medical field where it is used for mechanical deflection and deformation in the patient bones. Deformation can cause a change in the shape of patient bones and this medical protractor is the tool to measure the angle by which deformation has happened on patient’s bones.
Taking a look at its shape, the medical protractor design seems like a combination of a full-circle protractor and a two-arm bevel protractor. It consists of a full circular body with two arms attaching to it. One arm is a fixed arm and is a permanent part of the circular body. Another arm is the free rotating arm and it can freely rotate along 360 degrees on the circular body of the protractor.
Circular scale is provided at the outer most edge of the circular body and it is used to measure the angle of deformation in patient bones. Both arms also have scale with graduation marks on them for measuring linear distance.
Advantages of medical protractor:
- For the medical observation
- It is a simple, easy to read, and easy to use as a medical instrument
7. Bevel Protractor
An advanced and improved form of a simple protractor is the bevel protractor. This bevel protractor is not only used in the education sector like the semi-circle for learning how to mark angles but also like the full-circle model used by engineers to measure, mark, and draw angles in workshops and engineering drawings.
The most contrasting thing about the bevel protractor is it has 1 or 2 arms attached to its main body. These arms function to measure in a proper and accurate way, further, eliminating more error chances. By the arm sticking directly to the object’s surface, a proper way of measurement happens.
Bevel protractor with one arm is called a single-arm bevel protractor and a protractor with two arms is called a double-arm bevel protractor
– Single-Arm Bevel Protractor
The main body of the single-arm bevel protractor is like a semi-circle protractor with scale graduated on the other most edge. An arm is pivoted at the center of the body.
A semi-circle scale is also provided on it and the graduation are marked in such a way you can measure the angle from any side means from left to right and also from right to left. Take a look at the following photo.
The arm can rotate a full 360 degrees to measure any angle that ranges from zero to three hundred and eighty degrees.
Because it has a half-circle shape, the scale of the bevel protractor has a graduation from 0 to 180°. The arm length can vary as per manufacturer and application requirements.
– Double-Arm Bevel Protractor
A double-arm bevel protractor is similar to that of a single-arm bevel protractor. It also has a semi-circle body with an arm attached at the center of the base semi-circle body. The outermost semi-circle edge of the protractor has a scale with graduation marks in both directions meaning from left to right and right to left of the semi-circle scale.
The difference lies in the arm amount. Unlike the single-arm bevel protractor, the double arm bevel protractor has another arm attached to the semi-circular body of the protractor. This second arm is a fixed arm and its direction is made parallel to the base of the protractor.
Both fixed and moving arm of the double arm bevel protractor has scale with graduation in millimeters on them. These arms can measure linear distance as well as can be used to measure the angle between them.
Application of bevel protractor:
- Designed and used to measure and draw angles at very close tolerance
- Able to read an angle up to 5 arcminutes
- No battery requirement
– Vernier Bevel Protractor
Vernier bevel protractor is the advanced model of protractor that is able to give high precision and accurate reading.
This protractor consists of a main circular body that has a circular scale graduated on the outermost edge. As the name says, it provides a vernier scale attached to the main scale. Further, this vernier scale helps the measurement get higher resolution.
This protractor also features the blade and beam. The beam is a fixed part of the circular main scale body whereas the blade is the part of the vernier scale.
To measure with a vernier bevel protractor, the object to measure must be put between the beam and blade whereas the main scale and vernier scale display the reading of angle.
Advantages of vernier bevel protractor:
- Vernier bevel protractor provides an accurate reading with a high resolution of 1/20 of the degree
- It’s pretty easy to operate and read
- More accurate to measure the object’s angle since the arms stick directly to the surface.
– Optical Bevel Protractor
A more advanced and improved form of a bevel protractor is the optical bevel protractor. The optical bevel protractor performs all functions of the bevel protractor with greater precision and accuracy.
Optical bevel protractor is all similar to the bevel protractor and in addition to this, it has a protective covering over the circular glass scale. This covering performs the double function of protecting the protractor scale and helps hide the irrelevant graduation during the reading of the angle. This increases the precision of the optical bevel protractor over the conventional bevel protractor.
To further increase the precision of the optical bevel protractor, a magnifying glass is featured at the covering of the protractor. This magnifies the scale during the reading and thus making it easy for the operator to read the scale correctly.
Advantages of optical bevel protractor
- removes the limitation of simple mechanical bevel protractor with the help of its covering
- provides increased precision over simple mechanical bevel protractor with the help of its covering
- features a magnifying glass to increase the precision of the tool and make it easy for the operator to read the protractor
– Digital Sliding T Bevel Protractor
A digital sliding T bevel protractor is one instrument that we consider a type of protractor. It’s a completely digital system with a button to switch it on and off and a screen to display the angle measured.
It consists of two main body parts: a digital display unit and a blade circular rotating unit. The connection part between the blade and the display lets the rotation against each other and the blade has a cavity to provide space for sliding back and forth during angle measurement.
The example of this protractor is General Tools 828.
Advantages of sliding T bevel protractor
- Digital system means it’s easy to operate, understand and read during the angle measurement
- Adjustable blade length according to the object to measure
- No calculation or observation is needed to measure the angle
- Fast, accurate, and reliable tool for angel measurement
8. Digital Protractor
Single-arm and double-arm digital protractors are very similar to single and double-arm bevel protractors. The only difference is about displaying the reading. The digital protractor, either single arm or double arm, provides an LCD screen to show the reading instantly. On the other hand, the mechanical bevel protractor uses a half-circle plate (circular body with scale) that contains graduations and markings.
– Single-Arm Digital Protractor
As the name suggests, a single-arm digital protractor has a single arm/blade. If this protractor is set at 90 degrees, it will shape a T shape. The arm of this protractor arm will pivot along the measuring range.
It might be similar to a single-arm bevel protractor in terms of shape. However, the reading is electronic.
An example of a single-arm digital protractor is General Tools 1702.
– Double-Arm Digital Protractor
This model has two arms of the same length. If the two arms are set at 90 degrees, it will shape an L shape.
One of the arms contains an LCD screen to display the reading. The buttons are also available for certain functions such as zero point setting, etc. Simply put the object between the arms, clamp the object with the two arms properly, and then take the reading.
This type of protractor is the most familiar models currently on the market.
Protractor is a basic and simple geometrical instrument that we can employ to either measure or draw angles. Based on the design and working system, we classify them into 8 types of protractor.
The variance of protractors means the spreading of applications. Some of them are excellent in providing a higher resolution angle measurement. On the other hand, the basic half-circle makes the measurement of angle in a drawing easy although it has a low resolution of 1°.
To conclude, each type has its own application and advantages. If you have a need to draw or measure an object’s angle whether it’s a 2D or 3D object, this post may help you. Based on the user’s needs, you can check which one of the 8 models above is suitable for your project. It’s also important to note that matching the model with your work maybe not be enough, getting the best protractor product is also crucial as each product has a different quality.