What Are Car Screws Called? Automotive Fastener Types Guide

Primary Automotive Fastener Terminology

Car screws are most accurately referred to as automotive fasteners, a broad category that encompasses bolts, machine screws, self-tapping screws, clips, and specialty hardware specific to vehicle assembly. While "screw" is commonly used colloquially, technicians distinguish between threaded fasteners based on function: bolts mate with nuts or tapped holes in structural applications, machine screws secure components into pre-threaded metal, and self-tapping screws create their own threads in plastic or sheet metal. Modern vehicles contain over 3,000 individual fasteners, with Japanese manufacturers predominantly using metric JIS standards (e.g., M6x1.0) and American legacy models employing SAE/imperial sizes (e.g., 1/4"-20). Correct identification requires matching thread pitch, head style, drive type, and grade marking rather than relying on generic terminology.

Common Threaded Fastener Types and Applications

Automotive threaded fasteners are engineered for specific load, vibration, and corrosion requirements. Misidentifying these can lead to component failure or stripped threads during service.

Metric vs. Imperial Identification

Virtually all post-1990 vehicles use metric fasteners. Metric bolts are marked by diameter and pitch (e.g., M8x1.25), while imperial uses diameter and threads-per-inch (e.g., 5/16"-18). Using an incorrect pitch gauge can cross-thread aluminum components irreparably; always verify with a thread checker before installation. Grade markings differ too: metric bolts display strength class on the head (8.8, 10.9, 12.9), whereas SAE bolts use radial line patterns.

Non-Threaded Clips and Retainers

Modern vehicles rely heavily on non-threaded fasteners for trim, panels, and wire harnesses. These are frequently misidentified as "screws" but serve entirely different functions and require specialized removal tools. Common types include:

• Push-Type Rivets: Nylon or plastic expandable clips for fender liners, door cards, and underbody shields; identified by center pin diameter (typically 6mm, 8mm, or 10mm).
• Speed Nuts / U-Nuts: Spring steel cage nuts that clip onto sheet metal edges, providing reusable threaded points for body panels and bumpers without welding.
• Christmas Tree Clips: Multi-tiered barbed retainers for insulation, carpet, and headliners; named for their layered profile resembling a tree silhouette.
• Grommet Screws: Hybrid fasteners combining a metal screw with integrated rubber grommet for sealing and vibration isolation in firewall and floor pan penetrations.

These clips are model-specific and rarely interchangeable between brands. Always reference OEM part numbers or measure stem diameter and panel thickness precisely when sourcing replacements; generic assortments often fail due to dimensional tolerances exceeding ±0.3mm.

Critical Specifications: Torque, Coating, and Reusability

Automotive fasteners are not commodity hardware; they are precision-engineered components with strict performance criteria. Three specifications demand attention during any repair:

• Torque-to-Yield (TTY) Bolts: Used in cylinder heads, main bearings, and connecting rods; designed to stretch plastically during installation and must never be reused. Reusing TTY bolts risks clamping force loss and catastrophic engine failure.
• Corrosion Protection: Exterior and underbody fasteners feature zinc flake, dacromet, or geometric coatings rated for 720+ hours salt spray resistance. Substituting plain steel or inferior-coated hardware accelerates rust jacking and seizure.
• Prevailing Torque Features: Nyloc inserts, deformed threads, or adhesive patches prevent loosening under vibration. These features degrade after one installation cycle; replacement is mandatory per OEM service procedures.

Always consult factory service manuals for exact torque values and angle specifications. Generic charts risk overtightening aluminum components or undertightening safety-critical joints. When in doubt, replace questionable fasteners with OEM-specified parts rather than risking field failures.