Bolts and screws need materials with very high ultimate tensile strength (UTS) to carry heavy loads without breaking. In normal environments (room temperature, non-corrosive), the strongest materials are advanced metal alloys and fibers. Below we list top materials by tensile strength, distinguishing commercial alloys (actual fastener materials) from advanced or theoretical materials. Typical UTS values are given (in MPa or GPa) for comparison.

Commercial High-Strength Alloys

• High-Grade Alloy Steel (Class 8.8–12.9): Standard steel bolt grades reach UTS ≈800–1200 MPa (e.g. Metric 10.9 ≈1040 MPa, 12.9 ≈1200 MPa). These are common fasteners made by quenching and tempering.
• Tool Steels (e.g. D2, M2): Hardened cold-work tool steels can exceed ~2000 MPa. For instance, D2 tool steel is often ≥2000 MPa UTS when fully hardened, giving exceptional strength and wear resistance (though high carbon makes it brittle). These steels can be used in specialty bolts or inserts.
• Maraging Steels (18Ni alloys C300/C350): Ultra-strong aging steels achieve ~2000–2400 MPa. Maraging steel fasteners (Ni–Co–Mo alloys) are used in aerospace and high-performance applications, offering ~2.0–2.4 GPa UTS after aging.
• Titanium Alloys (e.g. Ti-6Al-4V Grade 5): Titanium fasteners offer ~900–1200 MPa UTS with excellent strength-to-weight. Ti-6Al-4V typically runs around 950 MPa (annealed) and up to ~1100–1200 MPa with heat treatment, making it much stronger than pure Ti. Titanium screws are common in aircraft and race cars for high strength without much added weight.
• Nickel Superalloys (Inconel 718, etc.): Nickel-based alloys are strong (~1000–1300 MPa) and corrosion-resistant. Inconel 718, for example, can have UTS around 1100–1300 MPa at room temperature. These are more often used in high-temperature environments, but at ambient they rival steel strength.
• Tungsten and Tungsten Alloys: Pure tungsten metal has one of the highest UTS among elements (~1500 MPa) but is very brittle, so it’s rarely used for conventional bolts. Tungsten heavy alloys (mixed with Ni/Fe) are tougher and can reach ~1000–1400 MPa, but these are specialized.
• High-Carbon Steels (e.g. 4340, 52100): Through hardening, steels like AISI 4340 or 52100 can approach ~1500–2000 MPa. Bearing steels (AISI 52100) and high-strength alloy steels (AISI 4340 in high hardness state) are known to reach ~1.5–2.0 GPa. These steels can be used in extremely high-strength fasteners or ball joints.

High-Performance Fiber Composites (Examples)

• Aramid Fibers (Kevlar, Twaron): Aramid yarns have tensile strength around 2.5–3.6 GPa. They’re much stronger than steel by weight but used in ropes, body armor, etc. (Not typical for threaded bolts, but often cited as high-strength fibers.)
• PBO Fiber (Zylon): PBO (Zylon) fibers boast ~5.8 GPa UTS – far above Kevlar. Again, these are specialty fibers used in cables and sails, not metal fasteners.
• Ultra-High-Molecular-Weight Polyethylene (Dyneema/Spectra): UHMWPE fibers reach ~3.5 GPa. They’re extremely light and strong, used in high-performance ropes and armor. Fasteners made of polymer fiber composites are not standard, but these fibers set a benchmark for strength.
• Carbon Fiber Reinforced Polymers: Carbon fibers can reach ~3–7 GPa in tension (depending on fiber type). Carbon-fiber composites have high strength-to-weight, used in aerospace panels and bike frames. They are rarely used for screw threads because composites typically lack ductility and thread durability.
• Advanced CNT/Graphene Fibers (Emerging): Research carbon nanotube (CNT) and graphene fibers have shown tens of GPa potential. Some CNT yarns are reported ~50–80 GPa in lab settings. These are not commercial fastener materials, but they highlight the extreme tensile capability of carbon nanomaterials.

Theoretical and Experimental Materials

• Graphene (Single-Layer Carbon): A perfect graphene sheet has a theoretical tensile strength ~130 GPa (130,000 MPa). This is orders of magnitude above any bulk material. Real graphene sheets (or papers) haven’t yet been formed into macroscopic bolts, but graphene sets the theoretical upper limit for carbon-based tensile strength.
• Carbon Nanotubes (CNTs): Individual CNTs have demonstrated tensile strength around 50–80 GPa. Bundles or yarns of aligned CNTs have achieved ~30–100 GPa in experiments. Like graphene, CNT materials are still in development and not used for standard fasteners.
• Diamond and Diamond Nanothreads: Diamond has an extremely high theoretical strength (on the order of 90–200 GPa depending on direction), but it is a brittle crystal. Diamond “nanothreads” (theoretical 1D diamond structures) are predicted ~30–50 GPa. Again, no real diamond bolts exist, but diamond provides a ceiling on material strength.
• Bulk Metallic Glasses (Amorphous Metals): Certain lab-made metal glasses show UTS in the range 2–6 GPa. They combine metal’s high density with glass-like structure. They are not widely used in fasteners (mostly coatings or small parts), but they illustrate very high achievable strength without a crystalline grain structure.
• Boron Nitride Nanotubes (BNNTs): Similar to CNTs, BN nanotubes could theoretically reach tens of GPa tensile strength. Research continues, but like carbon nanotubes these are not commercial materials yet.
• Graphene–Metal Composites (Experimental): Scientists are exploring adding graphene layers to metal, which could one day produce bolts much stronger than today’s alloys. This is cutting-edge research, with no commercial products yet, but it points to future possibilities beyond present materials.

Summary and Considerations

For practical bolts and screws, the strongest materials available today are specialized metal alloys. The top end is represented by maraging steels and quenched tool steels (UTS up to ~2.0–2.4 GPa) and hardened high-alloy steels (around 1.5–2.0 GPa). Modern aerospace/titanium fasteners hit ~1.0–1.2 GPa while saving weight. Even higher strengths (3–6 GPa) occur only in fiber composites (Kevlar, carbon fibers, UHMWPE) which are not used in typical threaded fasteners.

Materials like graphene or CNTs far exceed all commercial options (tens of gigapascals) but remain laboratory curiosities for now. In summary, bolts and screws today use steels and alloys in the 1–2 GPa range (available off-the-shelf), while future materials (graphene, CNTs, metallic glasses) hint at orders of magnitude higher strength that could one day revolutionize fasteners. The practical “limit” for standard fastener materials remains around 2–2.5 GPa for the foreseeable future.