CFS Blind Fasteners & Rivets 2 — Questions and Answers
Question 1: A 'Rivnut' (threaded insert or nutsert) is classified as a blind fastener because:
- It uses a breaking mandrel identical to standard pop rivets
- It is installed by pulling a threaded mandrel that deforms the insert body from one side, creating a nut thread (Correct answer)
- It requires no special installation tools
- It can only be installed in thin sheet metal under 1mm
Correct answer: It is installed by pulling a threaded mandrel that deforms the insert body from one side, creating a nut thread
A threaded insert (Rivnut/nutsert) is set by rotating and pulling a mandrel that collapses the insert body to grip the back of the panel, creating a reusable threaded hole from one side.
Question 2: According to IFI and industry standards, a blind rivet's nominal diameter is measured:
- Across the set head on the accessible side
- By the body (shank) outer diameter before installation (Correct answer)
- By the mandrel diameter after fracture
- Across the blind-side bulge after installation
Correct answer: By the body (shank) outer diameter before installation
The nominal diameter of a blind rivet refers to the outer diameter of the unset rivet body (shank), which corresponds to the drill size used for hole preparation.
Question 3: What failure mode is most likely when a blind rivet is installed in a joint that exceeds the rivet's maximum grip range?
- The mandrel will not fracture during setting
- The rivet body will not fully collapse, leaving the joint under-clamped with a loose mandrel stub (Correct answer)
- The rivet head will pull through the material
- The rivet body will fracture instead of the mandrel
Correct answer: The rivet body will not fully collapse, leaving the joint under-clamped with a loose mandrel stub
When the material stack exceeds the maximum grip, the rivet body does not deform enough to clamp the joint properly, resulting in a loose connection and a protruding or improperly broken mandrel.
Question 4: Which military or aerospace specification is commonly referenced for solid (non-blind) aluminum aircraft rivets, providing a baseline to which blind rivet specifications are often compared?
- NAS 1738
- MS 20470 (AN470) (Correct answer)
- ASTM A325
- SAE J429
Correct answer: MS 20470 (AN470)
MS 20470 (also known as AN470) covers the universal head solid aluminum aircraft rivet that is a foundational standard in aerospace fastening, distinguishing it from blind rivet specs.
Question 5: A 'drive rivet' (or hammer-set rivet) differs from a pull-type blind rivet in that it is set by:
- Pulling a mandrel with a pneumatic rivet gun
- Driving a pin into the rivet body with a hammer or press, expanding the blind end (Correct answer)
- Threading a bolt through the rivet body
- Applying heat to expand the rivet shank
Correct answer: Driving a pin into the rivet body with a hammer or press, expanding the blind end
Drive rivets are set by hammering or pressing a pre-installed pin into the rivet body, causing the blind end to splay and clamp the joint without needing a pull-type tool.
Question 6: For a tri-fold (3-leg) blind rivet design, what is the main engineering advantage over a standard single-bulge design?
- Three-fold rivets are smaller in diameter, reducing weight
- The three-petal blind-side flange distributes the clamp load over a larger area, improving performance in soft or thin materials (Correct answer)
- Tri-fold rivets are easier to remove and reinstall
- They are approved for use in flammable environments
Correct answer: The three-petal blind-side flange distributes the clamp load over a larger area, improving performance in soft or thin materials
The three folding petals of a tri-fold rivet create a wider bearing footprint on the blind side, reducing stress concentration and preventing pull-through in soft substrates like plastics or thin sheet metal.
Question 7: When inspecting a completed blind rivet installation, which visual indicator suggests the rivet has been properly set?
- The mandrel head is flush with or slightly below the rivet head face, with a fully formed blind-side bulge (Correct answer)
- The mandrel is still visible and protruding above the rivet head
- The rivet body shows longitudinal cracks along the shank
- The material shows slight buckling around the rivet
Correct answer: The mandrel head is flush with or slightly below the rivet head face, with a fully formed blind-side bulge
A properly set blind rivet will have the mandrel fractured at or just below the rivet head surface and a fully formed upset bulge on the blind side indicating correct clamp-up.
CFS Blind Fasteners & Rivets 2
A 'Rivnut' (threaded insert or nutsert) is classified as a blind fastener because: