Wing Nuts, Wing Screws and Thumb Screws: A Fastener That Saved a Production Line—And Nearly Destroyed One

The Complete Engineering Reference Guide to Types, Dimensions, Threads, and Points

A Fastener That Saved a Production Line—And Nearly Destroyed One

The conveyor belt had been down for forty-seven minutes.

the practitioner Medina, maintenance supervisor at a packaging facility outside of Monterrey, was watching money evaporate. Every minute of downtime cost the plant roughly the equivalent of a skilled worker's daily wage. The problem wasn't catastrophic—a single access panel on the shrink-wrap module needed to come off so a jammed roller could be cleared. But whoever had designed the enclosure had secured every panel with standard Phillips-head machine screws.

the practitioner's technician needed a driver. The driver was in the tool crib. The tool crib was locked. The night-shift supervisor who had the key was unreachable.

Forty-seven minutes. For a screw.

Six months later, after the practitioner convinced his plant engineer to redesign every frequently-accessed panel on the line, every one of those machine screws was replaced with wing screws—fasteners you tighten and loosen by hand, with no tools required.

Downtime for the same jam? Under four minutes.

This is the story of one of the most underappreciated fasteners in the engineering world. It's also the most complete reference you'll find on wing screw types, dimensions, materials, threads, and point styles—all governed by ANSI B18.17-1968 (R1983) and built to last across every industry that uses them.

What Exactly Is a Wing Screw?

A wing screw is a screw with a wing-shaped head designed for manual turning without a driver or wrench. The "wings" provide leverage surfaces for your fingers, allowing fast installation and removal in applications where frequent access, quick adjustment, or tool-free operation is essential.

Wing screws are classified by two criteria under ANSI B18.17-1968 (R1983):

• Type — based on the method of manufacture
• Style — based on design characteristics (wing height, construction details)

There are four types: A, B, C, and D. Each has distinct manufacturing processes, material options, and dimensional profiles. Understanding the differences isn't academic—it determines whether your fastener holds up in service or becomes the weak link in your assembly.

The Four Types of Wing Screws: Manufacturing, Materials, and When to Use Each

Type A — Cold Formed / Cold Forged Two-Piece Construction

Construction: Two-piece assembly with cold formed or cold forged wing portions of moderate height.

Series Available: Regular, Light, and Heavy (depending on size) — allowing you to match wing spread and grip to your specific application.

Materials: Normally supplied in carbon steel with the shank portion case hardened. Also available in corrosion resistant steel, brass, or other materials by agreement between manufacturer and user.

Best For: High-volume production environments where moderate wing height and case-hardened durability are priorities. The two-piece construction allows optimization of wing and shank materials independently.

Think of Type A as: The industrial workhorse. the practitioner's plant used Type A wing screws for their panel replacements because the case-hardened shank resisted the daily wear of repeated installation and removal cycles.

Type B — Hot Forged One-Piece Construction

Construction: One-piece, hot forged solid construction. Available in two wing styles:

• Style 1 — Wings of moderate height
• Style 2 — High wings (taller wing profile for increased finger leverage)

Materials: Normally made from carbon steel, but also available in corrosion resistant steel, brass, or other materials.

Best For: Applications demanding structural integrity where the one-piece forged construction eliminates any risk of wing separation. Style 2's high wings are ideal where operators wear gloves or need maximum finger purchase.

Think of Type B as: The heavy-duty option. When a colleague of the practitioner's at a steel fabrication shop needed wing screws for jig fixtures that got manhandled by welders in heavy leather gloves, Type B Style 2 was the only answer—tall wings that gloved fingers could actually grip.

Type C — Die Cast Construction

Construction: Available in two styles:

• Style 1 — One-piece die cast construction with wings of moderate height
• Style 2 — Two-piece construction with a die cast wing portion of moderate height and a separate shank

Materials:

• Style 1 — Supplied only in die cast zinc alloy (no other material options)
• Style 2 — Wing portion is die cast zinc alloy; shank portion is normally carbon steel, but may be corrosion resistant steel, brass, or other materials by agreement

Best For: Cost-sensitive applications with moderate duty requirements. Die casting allows complex wing geometries at scale. Style 2 gives you the economy of zinc alloy wings with the thread strength of a steel shank.

Think of Type C as: The economical specialist. A furniture manufacturer producing adjustable display fixtures chose Type C Style 2—zinc alloy wings looked clean on the showroom floor, while the steel shank provided the thread engagement strength needed for repeated retail adjustments.

Type D — Welded Two-Piece Construction

Construction: Two-piece welded construction with stamped sheet metal wing portions of moderate height.

Materials: Normally supplied in carbon steel, also available in corrosion resistant steel, brass, or other materials.

Best For: Applications where stamped metal wings provide adequate strength at lower cost than forging or die casting. The welded joint must be evaluated for your loading conditions.

Think of Type D as: The fabricator's choice. Light-duty access panels, enclosures, and non-structural assemblies where manufacturing economy matters more than extreme durability.

Quick-Reference: Wing Screw Type Comparison Matrix

Complete Dimensional Data: Types A and B Wing Screws

The following tables reproduce the complete dimensional data from ANSI B18.17-1968 (R1983), Table 5. All dimensions are in inches. Sizes shown in bold are preferred.

Key Dimensional Parameters:

• A = Wing Spread (the overall width across both wings)
• B = Wing Height (the height of the wing portion above the boss)
• C = Wing Thickness
• E = Boss Diameter (the cylindrical hub between the wings and the shank)
• G = Boss Height
• L = Practical Screw Lengths (Max and Min available)

Type A Wing Screws — Dimensional Table

Reading This Table: A 1/4-20 Type A wing screw in the Regular series uses a "C" blank with a wing spread between 1.12″ and 1.25″, wing height between 0.53″ and 0.66″, and is available in lengths from 0.50″ to 1.50″.

Type B Wing Screws — Style 1 (Moderate Height Wings)

Type B Wing Screws — Style 2 (High Wings)

Style 1 vs. Style 2 — The Critical Difference: Compare the 1/4-20 across both styles. Style 1 has a wing height of 0.50–0.56″. Style 2 jumps to 0.88–0.94″—nearly double the wing height for the same screw diameter. That extra height translates directly into finger leverage and grip accessibility.

Complete Dimensional Data: Types C and D Wing Screws

These dimensions come from ANSI B18.17-1968 (R1983), Table 6. All dimensions in inches.

Additional Parameters for Types C and D:

• E = Boss Diameter (upper)
• F = Boss Diameter (lower, where applicable)
• G = Boss Height
• L = Practical Screw Lengths (Max / Min)

Type C Wing Screws — Style 1 (One-Piece Die Cast)

Type C Wing Screws — Style 2 (Two-Piece Die Cast Wing + Steel Shank)

Type D Wing Screws — Dimensional Table

Design Insight: Notice that Type D wing screws have the smallest wing spreads of all four types at comparable sizes. A 1/4-20 Type D maxes out at 1.09″ wing spread, while a Type A Regular hits 1.25″ and a Type B Style 1 reaches 1.16″. For tight-clearance applications, Type D's compact profile may be exactly what you need. For maximum grip leverage, look elsewhere.

Threads for Wing Screws

All wing screw threads conform to the ANSI Standard Unified Thread, Class 2A.

Here are the critical details you need to know:

Thread Class and Plating Rules

• Unplated screws: Class 2A maximum diameters apply directly
• Plated screws (additive finish): Class 2A maximum diameters apply to the screw before plating; the basic diameters (Class 2A maximum diameters plus the allowance) apply to the screw after plating

This distinction matters enormously for quality control. If you're receiving plated wing screws and checking them against Class 2A maximums, you'll reject perfectly good parts. The allowance built into the Unified Thread system accounts for the plating thickness.

Thread Extent

All types of wing screws should have complete (full form) threads extending as close to the head or shoulder as practicable.

This means you can expect thread engagement right up to the underside of the wing boss—maximizing the clamping length available for your joint.

Standard Thread Sizes in the supplied reference

Practical Note: The UNC (Unified National Coarse) thread series dominates wing screw applications. Coarse threads are more forgiving of cross-threading during hand installation—exactly the scenario wing screws are designed for. You won't find UNF (fine) threads in standard wing screw offerings because fine threads punish the very hand-tightening behavior wing screws are built to support.

Points for Wing Screws: Six Options for Every Application

Wing screws are normally supplied with plain points—simple sheared ends. But the standard provides five alternate point styles, each serving a distinct engineering purpose. These are specified in ANSI B18.17-1968 (R1983), Table 8.

The Six Point Types

1. Plain Point (Default) A sheared end with no special geometry. Adequate for through-hole applications where the screw passes completely through the workpiece into a tapped hole or nut.

2. Cup Point A concave recess in the screw end that creates a sharp annular edge. The edge bites into the mating surface, providing excellent resistance to vibrational loosening. Used where the screw bears directly against a surface to prevent movement.

3. Cone Point A pointed conical end that seats into a matching conical recess or center-drilled hole. Provides precise, repeatable positioning. Used in jigs, fixtures, and alignment applications.

4. Dog Point A cylindrical pilot extending from the screw end. Fits into a corresponding hole in the mating part to provide shear resistance and alignment. The standard specifies that the axis of dog points shall not be eccentric with the axis of the screw by more than 3% of the basic screw diameter or 0.005″, whichever is smaller.

5. Flat Point A smooth, flat end perpendicular to the screw axis. Used where the screw bears against a surface without marring or indenting—common on polished or finished surfaces.

6. Oval Point A rounded, dome-shaped end. Provides a self-centering action when bearing against a surface, and is less likely to damage the mating part than a cup or cone point. Often used where repeated adjustment against the same surface is required.

Alternate Point Dimensions (Table 8, ANSI B18.17-1968, R1983)

All dimensions in inches.

Key Standard Note: The external point angles specified apply to those portions of the angles which lie below the thread root diameter. The angle within the thread profile may vary due to manufacturing processes.

Point Selection Decision Guide

Lengths: How Wing Screws Are Measured and Sized

The length of a wing screw is measured parallel to the axis of the screw from the intersection of the head (or shoulder) with the shank to the extreme point of the screw.

This is critical—you're measuring from the underside of the wing boss, not from the top of the wings. The wing height is not included in the "length" specification.

Standard Length Increments

The standard defines length increments by nominal screw size:

For sizes #4 through 1/4 inch:

• Nominal lengths 0.25″ to 0.75″ → increments of 0.12″ (approximately 1/8″)
• Nominal lengths 0.75″ to 1.50″ → increments of 0.25″ (1/4″)
• Nominal lengths 1.50″ to 3.00″ → increments of 0.50″ (1/2″)

For sizes 5/16 through 1/2 inch:

• Nominal lengths 0.50″ to 1.50″ → increments of 0.25″ (1/4″)
• Nominal lengths 1.50″ to 3.00″ → increments of 0.50″ (1/2″)
• Nominal lengths 3.00″ to 4.00″ → increments of 1.00″ (1″)

Design Tip: If your required grip length falls between standard increments, always round up to the next available length and use washers or spacers to fine-tune your clamping distance. Never specify a non-standard length unless you're prepared to pay for custom manufacturing.

How to Properly Designate Wing Screws on Drawings and Purchase Orders

Getting the designation right prevents receiving the wrong parts. The standard requires the following data in this exact sequence:

1. Nominal size (number, fraction, or decimal equivalent)
2. Threads per inch
3. Length (fraction or decimal equivalent)
4. Type (A, B, C, or D)
5. Style and/or Series (if applicable)
6. Point (if other than plain point)
7. Material
8. Finish

Designation Examples

10–32 × 1-1/4, Wing Screw, Type A, Heavy, Steel, Zinc Plated

0.375–16 × 2.00, Wing Screw, Type B, Style 2, Steel, Cadmium Plated

0.250–20 × 1.50, Wing Screw, Type C, Style 2, Zinc Alloy Wings, Steel Shank, Brass Plated

Notice the Type C Style 2 example specifies materials for both the wing portion and the shank portion separately. This is required because Style 2 is a two-piece construction with different materials for each component.

Materials and Finish: The Complete Reference