**3 Types of Fits-Clearance Fit,Transition Fit & Interference Fit Every Engineer must know:**The relationship between the hole and the shaft during the Assembly is called as Fit.The various parameters that can be included are Maximum Interference,Minimum Interference,Maximum Clearance,minimum clearance etc.In this article,I will be defining all these parameters w.r.t. the hole and shaft assembly.Each Fit in this article is represented by a condition which needs to be satisfied and extreme cases are shown w.r.t.the assembly.Read this article till end so that you can understand 3 types of fits briefly.

**3 Types of Fits-Clearance Fit,Transition Fit & Interference Fit:**

There are three types of fits:

- Clearance fit
- Interference fit
- Transition fit

The brief explanation of all these types of fits was presented below.

**1.Clearance fit:**

The dimensions of hole and shaft are such that always clearance or gap is existing between hole and shaft called as Clearance fit.

**Condition**: Hole size must be greater than Shaft size.

**Extreme Cases:**

- L.Hole v/s L.Shaft –>H>S —->Clearance Fit
- L.Hole v/s H.Shaft –>H>S—–>Clearance Fit
- H.Hole v/s L.Shaft –>H>S —->Clearance Fit
- H.Hole v/s H.Shaft –>H>S —->Clearance Fit

As Hole size is greater than Shaft size,it is called as Clearance Fit.

** Ex:** Used in all the mating assemblies.

Maximum Clearance = higher limit of the hole – lower limit of the shaft= Difference between minimum material limits. |

Maximum clearance is also called as worst case clearance in the clearance fit.

Minimum Clearance = lower limit of the hole – higher limit of the shaft.= Difference between maximum material limits. |

**2.Interference fit:**

Dimensions of hole and shaft are such that without the interference of external agency the Assembly of hole and shaft is not possible.

**Condition:** Shaft size must be greater than Hole size.

**External agency for assembly:**

a.Force/Pressure: that is by the application of force or pressure we can get the push fit.

b: Heating or Cooling:that is by the application of Heating or Cooling we can get the shrink fit.

**Extreme Cases:**

- L.Hole v/s L.Shaft –>S>H —->Interference is Required
- L.Hole v/s H.Shaft –>S>H —->Interference is Required
- H.Hole v/s L.Shaft –>S>H —->Interference is Required
- H.Hole v/s H.Shaft –>S>H —->Interference is Required

According to the Transition Fit,in all the 4 cases interference is required.Lets look at the Interference fit.

**Ex:** Used in non-mating assemblies like bearing bushes fitted into the bearing housing,key fitted into the key way etc.

Maximum Interference = higher limit of the shaft – lower limit of the hole.= Difference between maximum material limits. |

Minimum Interference=lower limit of the shaft – higher limit of the hole.= Difference between minimum material limits. |

The power transmission capacity of interference fit is defined based on minimum interference only.

**3.Transition Fit:**

The dimensions of hole and shaft are such that sometimes the Clearance fit and sometimes the Interference fit is produced called as Transition fit.

**Condition:**

According to the latest definition,if one of the component is lying in between higher and lower limits of the Other component produces transition fit.

**Extreme Cases:**

**Case 1:**

- L.Hole v/s L.Shaft –>H>S —->Clearance Fit
- L.Hole v/s H.Shaft –>H<S—–>Interference Fit
- H.Hole v/s L.Shaft –>H>S —->Clearance Fit
- H.Hole v/s H.Shaft –>H>S —->Clearance Fit

**Case 2:**

- L.Hole v/s L.Shaft –>H<S —->Interference Fit
- L.Hole v/s H.Shaft –>H<S—–>Interference Fit
- H.Hole v/s L.Shaft –>H>S —->Clearance Fit
- H.Hole v/s H.Shaft –>H<S —->Interference Fit

According to the above cases,the Transition fit sometimes produces Clearance Fit and Sometimes it is producing Interference Fit.

Therefore it is called as Transition Fit.

**Applications**:

Used for producing non-mating assemblies like fit between Piston and Piston rings of IC engine,coupling and coupling rings etc.

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This is the complete explanation of all the 3 types of fits which are proved by the conditions and Extreme cases.

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