| 1 | Hexagon Head Screw, Fully Threaded | External hexagonal head; wrench-driven; full thread to the head | Metric: M3–M24 Unified: commonly #4–1 in | General machinery assembly, brackets, guards, equipment frames and through-fastening where a full threaded length is useful | ISO 4017 ASME B18.2.1 for inch-series hex cap screws | Choose the correct property class, thread pitch and across-flats dimension for the mating nut or tapped hole. |
| 2 | Hexagon Head Screw, Partially Threaded | External hexagonal head; wrench-driven; unthreaded shank under the head | Metric: M5–M24 and larger Unified: commonly 1/4–1 in | Structural and machine joints that benefit from a plain shank for alignment, shear bearing or controlled thread engagement | ISO 4014 ASME B18.2.1 for inch-series hex cap screws | The grip length is critical; the unthreaded shank should match the joint thickness and clearance requirements. |
| 3 | Fine-Pitch Hexagon Head Screw | External hexagonal head; fine metric or UNF/UNRF thread | Metric fine pitch: commonly M8–M20 Unified fine series: UNF/UNRF | Automotive, hydraulic, instrumentation and compact assemblies requiring greater thread engagement or finer adjustment | ISO 8676 for metric fine-pitch hexagon head screws ASME B1.1 for Unified inch threads | Fine threads offer a smaller pitch and larger minor diameter than coarse threads, but require compatible nuts or tapped holes. |
| 4 | Hexagon Flange Screw | External hexagonal head with an integral circular flange under the head | Metric: commonly M5–M16 Other sizes depend on the selected standard | Sheet-metal assemblies, vehicle components, machinery and joints where the flange distributes clamping load | ISO 4162 DIN 6921 is commonly referenced in legacy specifications | The integrated flange can reduce the need for a separate washer; verify flange diameter, bearing surface and head style. |
| 5 | Socket Head Cap Screw | Cylindrical head with internal hexagon socket; driven by a hex key | Metric: commonly M2–M30 Unified: commonly #2–1 1/4 in | High-strength machinery, molds, robotics, tooling and assemblies with limited wrench clearance | ISO 4762 ASME B18.3 | Provides high clamp force in a compact head diameter; use a properly sized hex key to reduce socket damage. |
| 6 | Low-Head Socket Screw | Reduced-height cylindrical head with internal hexagon socket | Metric: commonly M3–M16 Size availability varies by standard | Compact machinery, covers, sliding components and locations with restricted overhead clearance | ISO 14580 | The reduced head height provides clearance savings but generally has lower head load capacity than a standard socket head cap screw. |
| 7 | Button Head Socket Screw | Low-profile rounded head with internal hexagon socket | Metric: commonly M3–M12 Unified sizes are available under applicable inch standards | Machine guards, consumer equipment, furniture hardware and assemblies requiring a smooth, low-profile appearance | ISO 7380-1 and ISO 7380-2 ASME B18.3 for applicable inch-series socket screws | Use where appearance and reduced protrusion matter; do not substitute for a high-strength socket cap screw without checking load requirements. |
| 8 | Countersunk Socket Screw | 90-degree countersunk head with internal hexagon socket | Metric: commonly M3–M16 Unified sizes depend on the applicable specification | Flush-mounted panels, sliding surfaces, tooling plates and assemblies where the screw head must sit below or level with the surface | ISO 10642 ASME B18.3 for applicable inch-series designs | The receiving hole must have the correct countersink angle and diameter; countersunk heads provide less load-bearing area than flat-bearing heads. |
| 9 | Hexagon Head Screw with Reduced Shank | External hexagonal head with a reduced-diameter unthreaded shank | Metric sizes and lengths depend on the selected design standard | Special-purpose machine joints, weight-sensitive equipment and applications requiring controlled clearance around the shank | DIN-based specifications may be used for special designs; dimensional requirements must be stated on the purchase drawing | Reduced shank geometry is not interchangeable with a standard hex screw; specify shank diameter, grip length and tensile class separately. |
| 10 | Hexagon Socket Set Screw | Headless body with internal hexagon socket; point may be flat, cone, cup or oval | Metric: commonly M2–M24 Unified sizes depend on point style and standard | Locking gears, pulleys, collars, knobs and shafts where a flush or headless fastening solution is required | ISO 4026: flat point ISO 4027: cone point ISO 4028: dog point ISO 4029: cup point ASME B18.3 for inch-series designs | Select the point style according to the shaft surface and required holding method; these screws are not intended to replace structural cap screws. |