Machine screws are among the most universally specified fasteners in industrial assembly, electronics, machinery, and construction hardware. Unlike self-drilling screws that cut their own threads, machine screws are designed to mate with pre-tapped holes or nuts, requiring precise dimensional consistency. For procurement teams and engineers, a reliable machine screw size chart is the starting point for every BOM (bill of materials). This article provides a comprehensive reference for carbon steel machine screw sizes, thread pitches, head types, and strength grades.
Metric and Imperial Size Standards
Machine screws follow two dominant dimensional systems: metric (ISO/DIN) and imperial (ANSI/ASME). A complete machine screw size chart must cover both, because global supply chains frequently require cross-referencing.
Metric machine screws (ISO 1207 / DIN 7985 / DIN 912). Sizes range from M2 to M12 in common industrial use. Each nominal diameter carries a standard coarse pitch and, for smaller sizes, a fine pitch option. The table below lists the most frequently specified metric sizes:
Imperial machine screws (ANSI/ASME B18.3). Common in North American equipment and legacy installations, imperial sizes use a gauge number system for diameters below 1/4 inch and fractional inches above:
When sourcing from international suppliers, buyers should confirm whether the machine screw size chart in the supplier's catalog follows ISO, DIN, or ANSI standards, as thread compatibility is not interchangeable.
Head Types and Drive Systems
A machine screw size chart is incomplete without head type specifications, because the head determines both the bearing surface and the tool required for installation.
Pan head. The most common machine screw head — slightly domed with a flat bearing surface. Suitable for general assembly where the mating surface is flat and a clean appearance is desired.
Flat countersunk head. Designed to sit flush with the mating surface after installation. The 90-degree countersink angle (ISO 7046 / DIN 7991) requires a corresponding chamfer in the workpiece.
Button head (DIN 7380). Low-profile dome shape with a wider bearing surface than pan head. Commonly used in furniture, electronics enclosures, and applications with limited clearance.
Hex socket head cap screw (DIN 912 / ISO 4762). Cylindrical head with an internal hex drive. Provides the highest torque transmission among machine screw head types and is the standard choice for machinery and precision equipment.
Drive systems include Phillips (PH), Slotted (SL), Hex Socket (Allen), and Torx (TX). The drive type must be matched to the installation tooling — a detail frequently overlooked in procurement specifications.
Carbon Steel Strength Grades and Surface Treatments
Carbon steel machine screws are classified by property class (ISO 898-1):
Grade 4.8 — low carbon steel, minimum tensile strength 420 MPa. General-purpose, non-critical assemblies.
Grade 8.8 — medium carbon steel, quenched and tempered, minimum 800 MPa. Most common industrial grade.
Grade 10.9 — alloy steel, quenched and tempered, minimum 1040 MPa. Heavy machinery and structural applications.
Grade 12.9 — highest strength, minimum 1220 MPa. Precision equipment and high-stress connections.
Standard surface treatments include zinc plating (clear or yellow), black oxide, and mechanical galvanizing. For outdoor or humid environments, zinc-nickel plating or hot-dip galvanizing extends corrosion protection.
Summary
A comprehensive machine screw size chart spans metric M2–M12 and imperial #4–3/8, covering thread pitch, head type, drive system, and strength grade. Specifying each parameter correctly ensures thread compatibility, structural integrity, and efficient procurement. When in doubt, request a full dimensional datasheet from the supplier and verify tolerance class (6g for metric, 2A for imperial) before placing a bulk order.
Your Carbon Steel Machine Screw Supplier
EC FASTENER manufactures and exports carbon steel machine screws in metric (M2–M12) and imperial (#4–3/8) sizes, covering pan head, flat head, button head, and hex socket cap types. Property classes 4.8, 8.8, 10.9, and 12.9 are available with zinc plating, black oxide, or custom surface treatments. We support wholesale orders, OEM packaging, and mixed-SKU container shipments with full DIN / ISO / ANSI standard compliance.
Contact us today for a complete machine screw size chart PDF and a wholesale quotation tailored to your project.