Types of Fits: How to Choose the Right Fits in Engineering | RapidDirect (2023)

Most engineered products are synced between two or more components that fit or slip over each other to deliver their primary functions. However, achieving this comes with understanding fits and the different types of fits used in mechanical engineering.

Types of Fits: How to Choose the Right Fits in Engineering | RapidDirect (1)

This article would explore what are the different types of fits. This will be in terms of the different types of fits you can use in your products’ designing stage. It will also introduce how you can choose the right one. Let’s dive right in.

Contents hide

I What is a Fit?

II Types of Fits

III How to Choose Suitable Fit for Your Projects

(Video) How to choose Engineering Fit | LIMIT, FIT & TOLERANCE

IV Conclusion

What is a Fit?

Engineered products sometimes come as components that must slip or press against each other to deliver their functions. Therefore, a fit is used to describe these dimensional relationships between the components. It is used to determine whether the components are loose or tight which aids in slipping or pressing property. Understanding what a fit comes with understanding certain terms, which are explained below.

The Hole and Shaft Basis System

Types of Fits: How to Choose the Right Fits in Engineering | RapidDirect (2)

Fits are either shaft or hole-based. A hole is a component’s internal feature that is cylindrical or not, while a shaft is a component’s external feature that is cylindrical or not.

The hole’s size is kept constant for a hole-basis system while the shaft is altered to determine the fit. The reverse is for the shaft-basis systems where the shaft size is constant, and the hole size is altered to determine the fit.

Note that CNC turning services is a precision machining method that can manufacture shafts with specific measurements, so this way makes it easier to get desired fits.

Fits and Tolerances

Fits and tolerances go together in determining the assemblage of the components of a product. Therefore, understanding both concepts will play a huge role in a successful assemblage. Tolerance is the difference between the max size and the mini size limit. It has a positive value and is represented by a number without a sign.

How to Name Different Fit Types in Mechanical Engineering

Understanding how they name the different types of fits is very important since it helps select the right types of fits for assembling a product.

According to the International Organization for Standardization, an alpha-numeric code names a particular fit and denotes the fit’s tolerance. The alphabet part of the code is for the hole or shaft.

A code with an upper-case letter is for the hole, while that of a lower-case letter is for the shaft. For example, based on the letter used, H7/h6 is a tolerance range for the hole (H7) and shaft (h6), respectively. This code will also allow engineers to identify the upper and lower size limit of the hole and shaft.

Types of Fits

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There are different fit types in mechanical engineering and each one is designed for different circumstances. According to ISO, there are three different types of fits used in manufacturing products.

(Video) Fits and Tolerances: How to Design Stuff that Fits Together

Clearance Fits

Types of Fits: How to Choose the Right Fits in Engineering | RapidDirect (4)

From its name, a clearance fit is used in situations that call for loose mating and components’ free movement. Therefore, they are ideal in making products whose components need to slide in and out with ease.

Clearance fits have a smaller shaft than the hole. This results in two conditions. One is a maximum clearance in which the shaft has the minimum diameter while the hole has its maximum diameter. The other is the minimum clearance in which the shaft is maxed, and the hole is minimum.

Clearance fits are further divided into five categories classified based on how loose they are. Below are the different types of fits under this category:

  • Loose Running Fit

These are clearance fits with the largest clearance used in places where accuracy is not important

  • Free Running Fit

These fits are for situations that require the movement of components with little consideration to accuracy.

  • Close Running Fit

These fits are for situations that require small clearance with regard to accuracy.

  • Sliding Fit

These fits have high accuracy and are for situations that require high accuracy and small clearance. Therefore, parts where they are used, can turn and slide freely.

  • Locational Clearance Fit

Locational Clearance fits have high accuracy but can only provide minimal clearance.

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(Video) Fit and Types of Fits - Clearance Fit / Interference Fit & Transition Fit (Animation)

Interference Fit

Types of Fits: How to Choose the Right Fits in Engineering | RapidDirect (5)

What’s an interference fit? It is also called a press fit or friction fit is a fastening of two components by pushing them together. The fastening occurs via many mechanisms, and it involves a substantial amount of force to the couple and uncouples the components. The mechanism also determines the different categories of interference fits to use.

In interference fit, the difference between the shaft’s maximum size and the hole’s minimum size is the Maximum Interference. Also, the difference between the shaft’s minimum size and the hole’s maximum size is the Minimum Interference.

Interference fits have three categories:

  • Press Fit

They have minimal interference as assembling is via cold pressing.

  • Driving Fit

These fits have a more prominent interference fit than press-fit, and it needs higher assembly force for cold pressing.

  • Forced Fit

Assembling components requires heating the parts with a hole and freezing the shaft. Therefore, disassembling can lead to broken parts.

Transition Fit

Types of Fits: How to Choose the Right Fits in Engineering | RapidDirect (6)

These fits fall between clearance and interference fits and are ideal for situations in which accuracy is very important. For example, they are ideal for aligning where the mating component must be joined with extreme precision.

Engineers and machinists also call transition fits slip or push-fit. When you compared them in terms of the degree of clearance, they have a larger clearance than an interference fit. However, the clearance is not enough to guarantee movement in the joint. You can say that transition fits provide clearance or interference fit depending on the situation.

Transition fit has two major forms:

  • Similar Fits

It leaves a small clearance or creates a small interference, and assembly is obtainable by using a rubber mallet.

  • Fixed Fits

It leaves a small clearance or creates a small interference. Assembly is possible using light force.

How to Choose Suitable Fit for Your Projects

Choosing the right types of fits for your projects depends on understanding several factors. Below are the important factors that you should watch out for:


Based on what you need, there are different types of fits ideal for different kinds of purposes. By going through properties such as accuracy and tolerance, exhibited by the different types of fits and the product’s proposed function, you should decide on the right fits for a project.

(Video) classification of fits | Types of Fits | Clearance fit |Interference fit |Transition fit


Before deciding on the right types of fits for your products, you should know your budget. For example, using fits with tighter tolerances will cost more than normal. Therefore, you must weigh your options carefully. It would be best to get a fit that delivers the right tolerance needed to perform its functions while reducing product development costs.


You must understand the concept of tolerance of a product to choose the right types of fits for such a product. You have to be specific about what you want. Also, you must also answer questions such as whether you want the components to rotate in a full circle or want them to be tight?

Another thing you also need to be careful about is the tolerance slack, which is the total maximum or minimum tolerance of a particular measurement. For example, you have to be careful about the aggregation of different parts’ tolerance to make up a single product. This is very important if the resulting tolerance is very high.


Many things surround using the different fit types in mechanical engineering and employing each within different mechanical applications. By going through this article, you will have a perfect understanding of a fit and its different types. The article also showed what you need to look out for to choose the right fits for your projects. Understanding what a fit does is not as important as knowing how to apply it.

While this article will drill into you the basic knowledge you can utilize in various design guides, you can also set your products apart by outsourcing to the right company. If you feel you need this, we at RapidDirect are in the best position to deliver quality and cost. With our engineering support, your product’s quality can shoot you over your competitors in no time.

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What are fits?

Therefore, a fit is used to describe the dimensional relationship between the components of a product. It is used to determine whether the components are loose or tight which is very important in various design guides.

What are the different types of fits?

There are different fit types in mechanical engineering, and each one is designed for different circumstances. According to ISO, the different types of fits in manufacturing products are Clearance fit, Transition fit, and Interference fit.


How do you choose fits and tolerances? ›

Tolerance is defined as the total permissible variation of a size. It is the difference between maximum limit and minimum limit of size. When two parts are to be assembled the relation resulting from the difference between their sizes before assembly is called a fit.

What are different types of fit explain with suitable figures? ›

The three main categories are: Clearance fit. Transition fit. Interference fit.

Why do people choose to be fit? ›

You'll feel more confident. Getting fit helps you to feel your absolute best - in mood and body. As you become stronger, achieve physical goals and feel more focused, your mood will soar. Before you know it, you'll be radiating confidence from the inside out.

What is a healthy fit? ›

Being fit is a way of saying a person eats well, gets a lot of physical activity (exercise), and has a healthy weight. If you're fit, your body works well, feels good, and can do all the things you want to do, like run around with your friends.

What are the four major types of fits? ›

Transition − Transition can be defined as it is a fit that always ensures some interference between the hole and the shaft in the coupling.
The types of fits
  • Clearance fit.
  • Interference fit.
  • Transition fit.
Jun 25, 2020

What is free fit vs close fit? ›

Each number or diameter of screw size has its own Close Fit or Free Fit, independent of threads per inch. Each fit is toleranced so that a threaded object can pass through the hole while the head of the object will not. Free fit has a larger allowance while Close Fit has a tighter allowance.

What is clearance fit vs interference fit vs transition fit? ›

Clearance fits are further classified into Slide fit, easy slide fit, loose running fit, close running fit, and free running fit. Transition fits are classified into push-fit and wringing fit. Interference fits are classified into force fit, tight fit, and shrink fit.

How do you determine the correct tolerance on a dimension? ›

Tolerance Basics

The tolerance is the difference between the maximum and minimum limits. This can be shown as upper and lower limits (0.2500/0.2498) or an allowable amount above and below a nominal dimension (0.2499 ±0.0001). Both methods define the same range—the tolerable band—of allowable dimensions rejected.

How do you determine tolerance? ›

TOLERANCE - Usually provide as a percentage of the expected value. It can be plus or minus. Tolerance = (Measured Value - Expected Value)/Expected Value. In the above case the Tolerance is (75.1-75.0) / 75 = 0.13%.

What is fit in engineering measurement? ›

In engineering terms, the "fit" is the clearance between two mating parts, and the size of this clearance determines whether the parts can, at one end of the spectrum, move or rotate independently from each other or, at the other end, are temporarily or permanently joined.

What is clearance fit and interference fit? ›

In a specific type of fit, the difference between hole size and shaft size is called allowance. Allowance is used to explain the difference between clearance fit and interference fit. Positive allowance specifies the clearance fit whereas negative allowance in a fit specifies the interference or force fit.

What are the different types of tolerance? ›

Tolerance can be unilateral or bilateral. A unilateral tolerance varies in only one direction, while a bilateral tolerance varies in both directions from the basic size.

Why are fit people more successful? ›

The fact is, when a person is being physically active their body goes into fight or flight mode. This response releases an endorphin called “Brain Derived Neurotropic Factor (BDNF)” that gives you the ability to think more clearly and better respond to business demands.

Does it matter if you are fit? ›

Having a high level of overall fitness is linked with a lower risk of chronic disease, as well as a better ability to manage health issues that do come up. Better fitness also promotes more functionality and mobility throughout one's life span.

Why is being fit important in the workplace? ›

Worksite Physical Activity Can Improve Employee Health and Save Money. Using worksite wellness programs that promote physical activity can help you create a healthier workforce, which can mean lower health care costs for both you and your employees.

What are the fit principles? ›

The FITT principles are an exercise prescription to help participants understand how long and how hard they should exercise. FITT is acronym that stands for Frequency, Intensity, Time, and Type. FITT can be applied to exercise in general or specific components of exercise.

What is a fit assessment test? ›

The Fit assessment measures an individual's interests and values and matches them to the work environment, providing information that can help determine how well a person aligns with occupations in an organization.

What is the difference between physically fit and healthy? ›

While the words “fit” and “healthy” are often used synonymously in everyday language, the terms have entirely separate meanings. Fitness describes the ability to perform a given exercise task, and health explains a person's state of well-being, where physiological systems work in harmony.

What is the difference between slip fit and interference fit? ›

While interference fits create tight assembly tolerances, slip fits are just the opposite—they can easily give you a self-locating assembly, making manufacturing easier when needing close alignment.

What is slip fit vs press fit? ›

Press fit bushings are used for applications where the pressure is extremely tight on a hole location. Press fit bushing mounting is commonly used where the bushing won't need to be replaced. Slip fit bushings are generally used in larger productions and operations.

What is a interference fit in engineering? ›

An interference fit, also known as a pressed fit or friction fit is a form of fastening between two tight fitting mating parts that produces a joint which is held together by friction after the parts are pushed together.

What is the difference between loose fit and relaxed fit? ›

What is the difference between loose fit jeans and relaxed fit jeans? The main difference between loose fit jeans and relaxed fit jeans is the amount of room in the legs. As we mentioned before, loose-fit jeans have a lot of room in the legs, while relaxed-fit jeans have less room.

What is a sliding fit? ›

a fit that enables one part to be inserted into another by sliding or pushing, rather than by hammering.

What is a running fit? ›

The intentional difference in dimensions of mating mechanical parts that permits them to move relative to each other. A free running fit has liberal allowance; it is used on high-speed rotating journals or shafts.

How do you determine bearing shaft and housing fit? ›

There are multiple factors to consider when selecting shaft and housing fits for each application:
  1. Whether the inner ring is rotating or not.
  2. What type of load the application is producing and its direction.
  3. Bearing bore and outside diameter.
  4. The application itself.

How many types of fit are there? ›

The types of fits depend upon the actual limit of the hole or shaft which can be divided into three categories which are: Clearance fit, Interference fit & Transition fit.

What are the different types of tolerance in engineering? ›

A tolerance is an acceptable amount of dimensional variation that will still allow an object to function correctly. Three basic tolerances that occur most often on working drawings are: limit dimensions, unilateral, and bilateral tolerances.

What are the 4 fundamental elements of GD&T? ›

Basics of GD&T

There are four components to making sure that your drawing indicates the geometric and size requirements of each feature. These four requirements are known as SLOF: size, location, orientation, and form.

What are 3 factors that influence tolerance? ›

There are four factors that define range of tolerance: time, place, situation, and culture.

What are standard CNC tolerances? ›

For CNC machining, the standard tolerance limit is set around +/-. 005” (0.127 mm). For reference, the thickness of a human hair is 0.002” (0.05 mm). The standard tolerance limit is a small number and in most cases, such a small difference between two parts that perform the same function may not even matter.

What is tolerance limit in engineering? ›

In mechanical engineering, tolerances set the allowable deviation from assigned dimensions. The use of tolerances helps to ensure that the final product is readily usable, especially if it is a part of a larger assembly.

What are three examples of tolerance? ›

Tolerance Examples
  • Accepting People's Traditions and Religions. ...
  • Accepting LGBTQI+ People. ...
  • Accepting People's Political Stances. ...
  • Yimbyism. ...
  • Inclusion of sub-cultural groups. ...
  • Tolerating dress codes. ...
  • Integrated schools. ...
  • Accepting people you don't get along with in the workplace.
Oct 17, 2022

How do you consider someone fit? ›

Experts define physical fitness as “one's ability to execute daily activities with optimal performance, endurance, and strength with the management of disease, fatigue, and stress and reduced sedentary behavior.” This description goes beyond being able to run quickly or lift heavy weights.

How do I know if I am perfectly fit? ›

Here are 10 signs you're in shape even if you think you aren't.
  1. Your heart rate is where it should be. ...
  2. You can keep up with your friends on a walk or jog. ...
  3. Your recovery time rocks. ...
  4. You exercise consistently. ...
  5. The physical aspects of parenting are a cinch. ...
  6. Stairs don't scare you. ...
  7. You can do a variety of workouts. ...
  8. You feel rested.
Apr 13, 2018

How can we tell if someone is fit? ›

To be physically fit you should have: 1) aerobic (cardiovascular) endurance, which is the ability of your heart and lungs to supply oxygen during sustained physical activity; 2) muscular endurance and strength to perform activity without fatigue and with the force needed to do the job; and 3) healthy body composition, ...

What are the 5 indicators of a fit person? ›

A: The five components of physical fitness are cardiovascular endurance, muscular strength, muscular endurance, flexibility and body composition, according to Fit Day.

Does being fit matter? ›

Being physically active can improve your brain health, help manage weight, reduce the risk of disease, strengthen bones and muscles, and improve your ability to do everyday activities. Adults who sit less and do any amount of moderate-to-vigorous physical activity gain some health benefits.

How can you tell if a person is not physically fit? ›

The visible signs include; obesity, labored breathing, mood swings, or chronic illness. Physiological signs include; irritability, insomnia, high blood pressure, diabetes, heart disease, malaise, or increased resting heart rate.

What is Fitt principle? ›

The FITT principle is an acronym that represents, Frequency, Intensity, Time, and Type. It can be prescribed to people to improve health, similar to pharmacologic intervention. You can easily remember the basic principles of exercise using the so-called FITT factors.

Is being fit genetic? ›

Genetics impacts all areas of fitness and performance, including muscles and strength. From sprinters who have genes allowing them to develop more fast-twitch muscle fiber to endurance runners with genetics dictating muscle contraction speeds, genes determine our abilities to some degree.


1. Limits and Fits: The ISO System
(Tabletop Machine Shop)
2. Tolerancing: Calculating Fits With Machinery's Handbook
(R. Dean Odell)
3. Calculating Fits from Fit Tables
(Ryan Weber)
(ASK Mechnology)
5. Limits, Fits and Tolerances - Learn in Details
(Prodac Labs)
6. Tolerance & Fits | Hole and Shaft Mates | Clearance & Interference Fit | Example | Beginner
(Dr. Gucci's Engineering Education)
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