Wire thread inserts repair/reinforce threads in soft materials. Two types: Free Running (FR) and Screw Locking (SL). FR Inserts: Standard internal thread without locking. Requires external methods for vibration resistance. Used in low-vibration repair/reinforcement. SL Inserts: Feature a deformed coil section creating friction with screw threads. Provides mechanical lock and vibration resistance without added devices. Critical for high-vibration applications (e.g., aerospace, engines). Both use diamond-shaped wire (stainless steel/bronze) with removable tang. Installation: Drill/tap oversized hole. Insert coil with type-specific tool. Break tang; check fit. Sized by nominal thread (M6, 1/4-20) and length. FR = standard threads; SL = critical vibration resistance.

A Heli-Coil (wire thread insert) is a diamond-profile coil of spring-tempered wire installed into a tapped hole to restore, reinforce, or create durable internal threads. Its key structural feature is the diamond-shaped wire cross-section, providing multiple load-bearing surfaces and inherent vibration resistance. Common materials include stainless steel (most frequent), phosphor bronze, carbon steel, and high-temp alloys. Surface treatments like PTFE, dry lubricants, or silver plating reduce friction or enhance corrosion resistance. Heli-Coils repair stripped threads, reinforce soft materials (aluminum, plastic), improve thread life, resist vibration loosening, and join dissimilar metals. Classified as Free-Running Inserts (STI) or Screw Locking Inserts (SBI) for vibration applications. Installation requires drilling oversize, tapping with a special tap, winding the insert in using a mandrel, and breaking off the tang. It provides permanent, high-strength thread replacement.

Abstract: Keenserts and Helicoils both reinforce threaded holes but differ fundamentally. Keenserts are solid sleeves with external locking keys driven radially into host material during installation, creating a permanent, vibration-resistant mechanical lock. Ideal for high-torque/vibration applications (e.g., aerospace), they offer superior pull-out strength but require destructive removal. Helicoils are spring-like wire coils that elastically expand when installed using specialized tools. They excel in soft materials (aluminum, plastic) and thread repairs, distributing load evenly for enhanced fatigue resistance while allowing non-destructive replacement. However, they provide lower axial strength than Keenserts. Selection depends on application: Keenserts for extreme vibration/safety-critical joints; Helicoils for soft substrates, repairs, or cost-sensitive projects where elasticity and serviceability are prioritized.

Self-tapping thread inserts permanently repair stripped or weak threads (e.g., in aluminum, plastic) by installing a hardened steel coil insert. The insert features internal machine threads and sharp external cutting edges. Installation involves drilling the damaged hole to a precise smooth diameter. The insert is then driven clockwise into this hole using a special tool. As it rotates, its hardened external edges act like a tap, shearing material from the hole wall. This displaced material flows into the coil's grooves, simultaneously forming new external threads on the insert and corresponding mating threads in the host material, locking it tightly. Often, a final locking coil deforms to prevent loosening, and a drive tang is broken off. The result is a durable steel sleeve with strong internal threads, distributing load effectively and often exceeding the original thread's strength, ready for the original screw or bolt.

A self-tapping insert is a cylindrical metal sleeve (typically stainless steel, carbon steel, or aluminum) that creates durable internal machine threads in soft or damaged materials like plastic, wood, or thin metal. It features sharp external threads that cut/form threads into a pre-drilled hole upon installation and precise internal threads to accept standard screws/bolts. Common models vary by internal thread size (e.g., M3-M12, #4-1/4") and external installation diameter. Surface finishes like zinc plating or passivation enhance corrosion resistance. Installation involves drilling a precise hole and driving the insert clockwise with a suitable tool (screwdriver, hex key, or mandrel) until seated. Key applications include repairing stripped threads, reinforcing soft materials (plastics/wood), enabling repeated assembly in products, and joining dissimilar materials across industries like automotive, aerospace, and electronics.