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MODULE 7 OF 8

Connecting and Fitting: Couplings, Magnetic Couplings, Fits, and Standard Parts

5 units · approx. 35 minutes total · Step 1 of 7

Getting Started

This module addresses two seemingly separate but related topics: how two shafts are connected—mechanically via couplings or non-contact via magnetic couplings—and how two components fit together when one is inserted into the other. Both revolve around the same question: how much clearance or interference a connection can have in order to perform its function reliably.

A calculation exercise on magnetic couplings, a matching exercise on ISO fits, flashcards, and a case study bring the theory to life; a self-test at the end shows whether you’ve mastered the material.

Learning Objectives – After completing this module, you will be able to:

  • Distinguish between rigid, elastic, torsionally rigid, and engageable couplings and calculate the rated torque;
  • Convert torsional backlash into a linear positioning error and distinguish between backlash-free and backlash-prone components;
  • Distinguish between synchronous (permanent magnet) and hysteresis couplings and calculate the slip power;
  • interpret an ISO fit designation such as H7/k6 and identify the corresponding clearance, transition, and interference fits;
  • Match common shaft-hub connections and standard parts to their applications.

Learning units

Five short learning units (6–8 minutes) with learning objectives, examples, and knowledge checks—standalone learning content for this module, maintained independently of the website’s guides. Progress is saved locally in this browser.

0 of 5 units

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Computer Exercise 1: Design a magnetic coupling

A drive delivers P = 3 kW at n = 1,500 min⁻¹. A safety factor of S = 2.0 is specified for the magnetic coupling.

Calculate the load moment M_Last and the required transmission torque M_erf.

For verification: Magnetic coupling calculator (opens in a new tab)

Exercise 2: Match ISO fits

Match each fit with the correct fit type, and then click "Check."

H7/g6
H7/k6
H7/p6

For further reading: ISO fits H7/H6 (opens in a new tab)

Flashcards: Coupling and Magnetic Coupling Terms

Eight technical terms from the glossary—click on the card (or press Enter or the spacebar) to see the definition.

Flashcards

Tap to see the definition.

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Zero backlash
A state in which there is no measurable mechanical play in a drive element or guide—the fundamental prerequisite for high-precision positioning, minimal reversal errors, and maximum stiffness. Source: Glossary “Zero backlash”
Backlash (j)
The backlash j is the distance between the load-bearing and non-load-bearing flanks of two meshing gears. It is necessary for lubrication, accommodating thermal expansion, and maintaining manufacturing tolerances. Excessive backlash leads to backlash and noise; insufficient clearance can cause jamming. Source: Glossary “Backlash (j)”
Magnetic coupling
A magnetic coupling transmits torque contactlessly via a magnetic field from a drive shaft to a driven shaft—without mechanical contact and thus without wear on the power transmission itself. Source: Glossary “Magnetic coupling”
Permanent-magnet coupling (synchronous coupling)
The permanent-magnet coupling—also known as a synchronous coupling—features permanent magnets on both sides that engage pole-to-pole. It transmits torque synchronously and without slippage until the pull-out torque is exceeded. Source: Glossary “Permanent-magnet coupling (synchronous coupling)”
Hysteresis coupling
The hysteresis coupling transmits its torque via a hysteresis material rather than through fixed pole pairs. As a result, it delivers a nearly constant torque that is independent of speed—even under continuous slippage. Source: Glossary “Hysteresis coupling”
Containment shell (barrier wall)
The containment shell—also referred to as a boundary wall at TEA—is the non-magnetic wall between the inner and outer rotors of a magnetic coupling. It hermetically seals the conveyed medium from the drive side and is therefore the safety-critical component. Source: Glossary “Containment shell (barrier wall)”
Air gap
The air gap is the distance between the inner and outer rotors of a magnetic coupling—including the wall thickness of the containment shell. It is the most important control variable for the transmissible torque. Source: Glossary “Air gap”
Pull-out torque
The pull-out torque—also known as the slip torque—is the maximum torque that a magnetic coupling can transmit before the magnetic coupling breaks down and the coupling slips. Source: Glossary “Pull-out torque”

Case Study: Pump for Corrosive Fluids

A chemical plant uses a centrifugal pump to transport concentrated hydrochloric acid containing chloride. Over the past two years, the existing mechanical seal has caused several unplanned shutdowns due to leakage; furthermore, the pump is located in a part of the plant that is difficult to access. The plant manager asks TEA whether a magnetic coupling with a containment shell is the solution—and which containment shell material is suitable for this medium.

Key Questions

  1. Why is standard stainless steel unsuitable for the containment shell when used with hydrochloric acid containing chloride, and which materials are suitable instead?
  2. What advantages does the magnetic coupling offer over the conventional mechanical seal for this medium and this hard-to-access system?
  3. Is the magnetic coupling maintenance-free after the conversion?
View Worked Solution

1. Standard stainless steel (1.4571) is susceptible to pitting corrosion when exposed to chloride-containing or highly acidic media and should not be used in such applications. Hastelloy (highest corrosion resistance to acids and halides) or ceramics (chemically nearly inert and, additionally, loss-free) are suitable alternatives.

2. The magnetic coupling has no shaft passage and is leak-free when the containment shell is intact—unlike the mechanical seal, which has a system-related minimum leakage rate. The elimination of the risk of unplanned downtime and the elimination of containment measures (double seals, barrier fluid) for the aggressive medium are particularly valuable in systems that are difficult to access.

3. No. It requires significantly less maintenance, but it is not maintenance-free: The containment shell must be inspected regularly for corrosion, erosion, and cracks; in addition, the inner rotor bearings must be checked, and—in the case of a metal containment shell—thermal monitoring of eddy-current losses is required.

Technical basis exclusively: Magnetic coupling vs. mechanical seal (opens in a new tab) and magnetic coupling with containment shell (opens in a new tab)

Self-test

10 questions about this module—immediate feedback with explanations and source links. The module is considered complete if you score 7 out of 10 points or higher.

Self-test

10 questions for this module. You see right after each answer whether it was correct.

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Before each answer, you state how confident you feel. This helps distinguish knowledge gaps from uncertainty. It has no effect on the score.

Question 1 of 10

Question 1 of 10

According to the learning unit, which service factor S_B is typically used for applications involving heavy impacts (e.g., presses, hammers)?

Explanation

For severe shocks, the guide specifies a service factor of S_B from 2.5–4.0 – which is significantly higher than the 1.0–1.5 for uniform operation.

Source: Couplings in Mechanical Engineering →
Question 2 of 10

According to the comparison table, which coupling type achieves a torsional backlash of less than 0.5 arcmin?

Explanation

The metal bellows coupling, featuring a pleated stainless steel bellows, achieves torsional backlash values below 0.5 arcmin—the standard in high-precision robotics and medical technology.

Source: Couplings in Mechanical Engineering →
Question 3 of 10

What is the approximate linear positioning error caused by a torsional backlash of 5 arcmin with a lever arm of 1 m?

Explanation

s ≈ R · φ = 1,000 mm · 5 · 2.909 · 10⁻⁴ ≈ 1.45 mm – already unacceptable for high-precision applications.

Source: Zero Backlash vs. Backlash →
Question 4 of 10

According to the learning unit, which coupling design is best suited for maintaining constant web tension when winding material?

Explanation

The hysteresis coupling delivers a constant, speed-independent slip torque even under continuous slip—exactly what is needed to maintain uniform web tension in winders and unwinding systems.

Source: Hysteresis Coupling vs. Permanent-Magnet Coupling →
Question 5 of 10

Which material for the containment shell completely eliminates eddy-current losses?

Explanation

Ceramics are electrically non-conductive, so no eddy currents are generated in the rotating magnetic field—ideal for high speeds or critical efficiency requirements, but prone to brittle fracture.

Source: Magnetic coupling containment shell →
Question 6 of 10

What type of fit is H7/g6?

Explanation

H7/g6 is a clearance fit: The tolerance zone of the bore completely overlaps that of the shaft, resulting in positive clearance—typical for plain bearings and guide pins.

Source: ISO fits H7/H6 →
Question 7 of 10

What fit does the guide recommend for a rolling bearing outer ring that is to be axially movable as a non-locating bearing?

Explanation

G7 is a clearance fit with more clearance than H7 and is the standard for floating bearings, whose outer ring must be able to move axially to compensate for thermal expansion.

Source: Shafts and Bearings: Understanding Fits →
Question 8 of 10

Which statements are correct? (Multiple choice)

Explanation

H7/p6 always produces an interference fit (A correct), and DIN 740 specifies the service factors for flexible shaft couplings (C correct). The direction of the load is decisive: The ring subjected to a circumferential load (usually the rotating one) is given a tight fit with an interference fit, while the ring subjected to a point load is given a loose fit (B incorrect); the magnetic coupling is leak-free only as long as the containment shell remains intact (D incorrect).

Source: ISO fits H7/H6 →
Question 9 of 10

A motor delivers P = 2 kW at n = 750 min⁻¹. What is the rated torque M_N in Nm?

Nm
Explanation

M_N = 9550 · P / n = 9550 · 2 / 750 ≈ 25.5 Nm.

Source: Couplings in Mechanical Engineering →
Question 10 of 10

A hysteresis coupling transmits M_Last = 6 Nm at a slip speed Δn = 350 min⁻¹. What is the slip power P_S in watts?

W
Explanation

P_S = M_Last · Δn / 9.55 = 6 · 350 / 9.55 ≈ 219.9 W.

Source: Magnetic Coupling Calculator →

Advanced Topics (optional)

The eight guide articles in this module, in case you’d like to delve deeper. Reading them is not required for the learning units and self-test in this module.

Curriculum v0.1 (Beta) · As of 17.09.2026 · content carefully prepared and reviewed – final sign-off to follow

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