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Question

Difficulty: HardBolts, Nuts, and Washers

A mechanic is securing a heavy steel mounting bracket to a vehicle frame rail using a standard vibration-resistant through-bolt fastener assembly. Arrange the components in the correct physical sequence along the fastener axis, starting at the bolt head insertion side and proceeding to the threaded end. In what sequence must these components be assembled from the bolt head to the securing nut?

  1. 1Hex head cap bolt
  2. 2Plain flat washer (head side)
  3. 3Mating structural steel plates (bracket and frame rail)
  4. 4Helical split-ring lock washer (nut side)
  5. 5Finished hex nut

Answer

Hex head cap bolt → Plain flat washer (head side) → Mating structural steel plates (bracket and frame rail) → Helical split-ring lock washer (nut side) → Finished hex nut
In a standard through-bolted mechanical assembly, the load path begins at the bolt head, passes through a flat washer that distributes clamping pressure, penetrates the joined workpieces, engages a split-ring helical lock washer on the nut side to maintain continuous spring preload against vibration, and terminates at the hex nut which applies the tightening torque.

Step-by-Step Solution

1
Identify the head-side fastener components and primary load distributor.
Position the plain flat washer over the shank directly against the bearing surface of the hex head cap bolt.
Flat washers distribute axial preload over a broader surface area and prevent the rotating bolt head from galling the workpiece surface during tightening.
2
Pass the bolt shank through the clearance holes of the mating components.
Align and sandwich the bracket flange and structural frame rail over the bolt shank.
The structural joint members must be centered within the grip length of the through-bolt.
3
Install the vibration-retention device and securing fastener onto the protruding threaded shank.
Slide the helical split-ring lock washer onto the bolt shank against the inner workpiece face, followed by the finished hex nut.
The lock washer must seat directly beneath the turned nut so its deflected spring edges bite into the nut bearing face to resist rotational loosening under cyclic mechanical vibration.

Key Concept

Proper mechanical through-bolt joint stackup and washer positioning
Estimated Time:1m 15s
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Topics

Bolts, Nuts, and Washers

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