External Drives

The drive type determines how torque is transferred from your tool to the fastener. Choosing the right drive affects installation speed, torque capacity, cam-out resistance, and security. This guide covers every drive type you'll encounter, from common to specialized.

External Drives

External drives use tools that grip the outside of the fastener head.

Hex (Wrench/Socket)

Profile: Six-sided external head engaged by wrenches, sockets, or adjustable wrenches.

Description: The most common external drive, offering excellent torque transfer and multiple tool options. Standard hex uses wrench sizes matching bolt diameter conventions; heavy hex uses one size larger.

Tool Requirements:

• Combination wrench
• Socket and ratchet
• Adjustable wrench
• Impact wrench/socket

Advantages:

• Maximum torque transfer—no cam-out possible
• Multiple tool options for any situation
• Visual confirmation of proper seating
• Easy to inspect for loosening
• Available in every grade and material

Disadvantages:

• Requires clearance for tool swing
• Rounded corners can strip with worn tools
• Head must remain accessible

Best For: Structural applications, high-torque requirements, machinery, anywhere maximum clamping force is needed.

Square (External)

Profile: Four-sided external head.

Description: Historical predecessor to hex. Rarely used today except in specialty applications. Provides positive engagement but fewer contact points than hex.

Advantages:

• Very positive engagement
• Simple manufacturing

Disadvantages:

• Largely obsolete
• Fewer tool options
• Less common than hex

Best For: Restoration, specialty applications, lag screws in some regions.

External Torx (6-Lobe)

Profile: Six-pointed star pattern on external head.

Description: Star-shaped external drive providing better torque transfer than hex with more contact points. Increasingly common in automotive applications.

Advantages:

• Higher torque capacity than hex
• Less prone to rounding
• Positive engagement

Disadvantages:

• Requires Torx sockets
• Less common in general hardware

Best For: Automotive, high-performance applications requiring compact high-torque fastening.

Internal Drives

Internal drives use tools inserted into a recess in the fastener head.

Hex Socket (Allen)

Profile:

Description: Six-sided internal recess driven by hex keys (Allen wrenches) or hex bits. Standard drive for socket cap screws. Provides excellent torque transfer in a compact package.

Tool Requirements:

• L-shaped hex keys (Allen wrenches)
• Hex bit + driver
• Ball-end hex keys for angled access

Sizes: Metric (1.5mm–19mm) and Imperial (1/16"–3/4")

Advantages:

• High torque capacity
• Compact head possible
• Tools are inexpensive and universal
• Ball-end versions allow angled drive
• Tamper-resistant when recessed

Disadvantages:

• Socket can strip with worn/wrong-size tool
• Debris can clog recess
• Requires correct size—no adjustability

Best For: Machinery, precision equipment, high-strength applications, anywhere compactness matters.

Phillips

Profile:

Description: Cross-shaped recess designed to cam out under excessive torque. The most common internal drive worldwide. Developed in the 1930s for automated assembly.

Sizes: #0, #1, #2, #3, #4 (most common: #2)

Tool Requirements:

• Phillips screwdriver
• Phillips bit + driver

Advantages:

• Self-centering design
• Widely available
• Works with power drivers
• Inexpensive

Disadvantages:

• Designed to cam out—damages head under high torque
• Wears quickly with power driving
• Requires correct size to prevent damage

Best For: General assembly, electronics, woodworking, applications where controlled torque matters more than maximum torque.

Slotted (Flathead)

Profile:

Description: Simple straight slot. The original screw drive, dating back centuries. Still used where simplicity or traditional appearance is desired.

Tool Requirements:

• Flat-blade screwdriver
• Slotted bit

Advantages:

• Universal—any flat blade works
• Easy to clean
• Traditional appearance
• No special tools needed

Disadvantages:

• Very prone to cam-out
• Screwdriver slips out easily
• Poor torque transfer
• Difficult for power driving
• Easily damaged

Best For: Decorative hardware, electrical terminals, restoration work, situations where any tool must work.

Pozidriv (PZ)

Profile:

Description: Improved Phillips with additional small ribs between main cross arms. Provides better grip and higher torque with reduced cam-out. Common in Europe.

Sizes: PZ0, PZ1, PZ2, PZ3, PZ4

Tool Requirements:

• Pozidriv screwdriver
• Pozidriv bit + driver

Advantages:

• Higher torque than Phillips
• Reduced cam-out
• Better power-driving performance
• Self-centering

Disadvantages:

• Not compatible with Phillips drivers
• Less common in North America
• Requires correct size

Best For: European equipment, production assembly, anywhere better torque than Phillips is needed.

Torx (6-Lobe / Star)

Profile:

Description: Six-lobed star pattern providing excellent torque transfer with minimal cam-out. Originally developed for automotive, now widespread in electronics, construction, and machinery.

Common Sizes:

Advantages:

• Excellent torque transfer
• Minimal cam-out
• High-speed power driving
• Long tool life
• Multiple contact points distribute stress

Disadvantages:

• Requires Torx drivers
• More expensive than Phillips
• Recess can collect debris

Best For: Automotive, electronics, decking, construction, anywhere high torque and fast assembly are needed.

Torx Plus

Profile: Similar to Torx but with shorter, stubbier lobes and tighter tolerances.

Description: Enhanced Torx design providing even higher torque capacity. The shallower, blunter lobes create more contact area and resist wear better.

Advantages:

• 20% higher torque than standard Torx
• Longer tool life
• Better high-volume production performance

Disadvantages:

• Not backward-compatible with standard Torx
• More expensive
• Less available

Best For: High-volume production, automotive assembly lines, aerospace applications.

Square (Robertson)

Profile:

Description: Square tapered recess invented in Canada. Provides excellent grip with virtually no cam-out. Standard in Canada, gaining popularity in US woodworking.

Sizes: #0 (yellow), #1 (green), #2 (red), #3 (black)

Advantages:

• Best cam-out resistance of common drives
• Self-centering
• Screws stay on bit (one-handed driving)
• High torque capacity
• Long tool life

Disadvantages:

• Less common outside Canada
• Requires Robertson bits
• Limited size range

Best For: Woodworking, deck screws, cabinet making, production assembly, anywhere cam-out resistance matters.

Tri-Wing

Profile:

Description: Three slotted wings radiating from center. Designed as a tamper-resistant drive for electronics and appliances.

Advantages:

• Moderate security
• Tools less commonly available to consumers
• Distinctive appearance

Disadvantages:

• Limited torque capacity
• Specialized tools required
• Recess can damage easily

Best For: Video game consoles, cell phones, small appliances, consumer electronics.

Spanner (Snake-Eye / Pig-Nose)

Profile:

Description: Two small holes requiring a special two-pronged driver. Common security drive for public installations.

Advantages:

• Good tamper resistance
• Simple design
• Difficult to improvise tools

Disadvantages:

• Low torque capacity
• Holes can strip
• Specialized driver required

Best For: Bathroom fixtures, public installations, vending machines, electrical panels.

One-Way (Security)

Profile:

Description: Slotted head with angled edges that allow driving in but not removal. Permanent installation drive.

Advantages:

• Cannot be removed with standard tools
• Permanent installation
• High security

Disadvantages:

• Extremely difficult to remove
• Low torque capacity
• No adjustment after installation

Best For: Permanent security installations, license plate fasteners, prison equipment, anti-theft applications.

Drive Type Comparison

Drive Selection Guide

For Maximum Torque

Choose: Hex (external), Hex Socket, Torx, Square (Robertson)

For Production Speed

Choose: Torx, Square (Robertson), Pozidriv

For General Purpose

Choose: Phillips, Hex Socket

For Security

Choose: Spanner, One-Way, Torx Security (pin-in-center), Hex Security

For Cost Efficiency

Choose: Phillips, Slotted, Standard Hex

For Woodworking

Choose: Square (Robertson), Torx, Star-drive composite

Tips for Drive Selection

1. Match driver to fastener exactly. Wrong-size drivers cause damage and stripped heads.

2. Consider assembly method. High-speed production favors Torx and Robertson. Hand assembly can use Phillips.

3. Factor in serviceability. If fasteners need periodic removal, avoid one-way and choose high cam-out resistance.

4. Security is relative. Determined attackers can obtain most "security" drivers. True security requires additional measures.

5. Regional standards matter. European equipment often uses Pozidriv. Canadian products favor Robertson.

Questions about drive selection for your application? Our technical team can recommend the optimal drive type for your needs.