CFS CFS Fastener Head Styles & Drive Types 2 — Questions and Answers
Question 1: What is the primary advantage of a hex flange head fastener over a standard hex head fastener?
- Higher tensile strength
- Integrated flange acts as a built-in washer, distributing load and reducing the need for a separate washer (Correct answer)
- Easier to cam out when overtightened
- Smaller overall head height
Correct answer: Integrated flange acts as a built-in washer, distributing load and reducing the need for a separate washer
The flange on a hex flange head extends radially from the hex body, providing a larger bearing surface that distributes clamping load and often eliminates the need for a separate flat washer.
Question 2: Which drive type offers the highest torque transfer capability and best resistance to cam-out among common drive styles?
- Slotted
- Phillips
- Torx (6-lobe) (Correct answer)
- Hex socket (Allen)
Correct answer: Torx (6-lobe)
Torx (6-lobe) drives engage the fastener walls with vertical flanks rather than angled ones, enabling higher torque transfer and virtually eliminating cam-out compared to slotted or Phillips drives.
Question 3: A 'Pozidriv' drive is most accurately described as:
- An improved Phillips drive with additional ribs between the four main wings to reduce cam-out (Correct answer)
- A proprietary Torx variant with eight lobes
- A one-way slotted drive for tamper resistance
- A square drive used exclusively in Canada
Correct answer: An improved Phillips drive with additional ribs between the four main wings to reduce cam-out
Pozidriv is an evolution of the Phillips drive that adds four secondary radial ribs at 45° to the main wings, significantly reducing cam-out and improving torque transfer.
Question 4: Which of the following head styles is most commonly specified for structural steel bolted connections per AISC and RCSC standards?
- Pan head
- Heavy hex head (Correct answer)
- Button head
- Truss head
Correct answer: Heavy hex head
Heavy hex head bolts have larger head dimensions than standard hex heads, providing greater bearing area and wrench engagement required for high-strength structural bolting per AISC/RCSC specifications.
Question 5: What is the purpose of a 'tamper-resistant' or 'security' drive, such as a pin-in-Torx or one-way slotted fastener?
- To increase torque capacity
- To prevent unauthorized removal using standard tools (Correct answer)
- To allow higher installation speeds
- To reduce galling in stainless steel fasteners
Correct answer: To prevent unauthorized removal using standard tools
Tamper-resistant drives require special tools for removal, deterring unauthorized disassembly in public fixtures, electronics, and security-sensitive installations.
Question 6: A fillister head screw is best characterized by:
- A flat countersunk bearing surface
- A tall cylindrical head with a small diameter and deep drive recess (Correct answer)
- A wide low-profile domed head
- A hex exterior with a slotted top
Correct answer: A tall cylindrical head with a small diameter and deep drive recess
Fillister heads are tall, narrow cylindrical heads with a relatively deep drive recess, making them useful where head height is not restricted and a deep slot or recess depth is needed.
CFS CFS Fastener Head Styles & Drive Types 2
What is the primary advantage of a hex flange head fastener over a standard hex head fastener?