Formerly Emhart Teknologies & Infastech

Wire Thread Insert Overview

Spiralock wire thread inserts are helically coiled fastening devices that provide permanent, wear-resistant screw threads that exceed the strength of most parent material; the inserts are designed to protect tapped holes against failures due to stripping, seizing, corrosion, and wear. Spiralock inserts are unlike any other wire thread insert for the fact that our inner diameter wire geometry incorporates our 30° wedge ramp thread form design. Our wire thread inserts are available in two styles: tanged and Drive Notch (DN®), engineered with no tang.

Crest of bolt seats against ramp of Spiralock insert thread profile, preventing transverse movement of bolt relative to insert, thus resisting loosening due to vibration.

Bolt Assembly Bolt Assembly
Standard Thread Insert

Standard Thread Insert

Spiralock Thread Insert

Spiralock Thread Insert

Features of the Spiralock wire thread insert:

  • Threads into (Screw Thread Insert) STI holes per NASM33537
  • Accepts standard 2A/3A bolts (4g6g and 6g)
  • Replaces Helicoil® locking inserts
  • Spiralock insert meets or exceeds the applicable parts of NASM8846, e.g. the wire tensile strength, chemical composition, and methods of inspection
  • Spiralock insert is not a prevailing torque-type screw-locking insert—no risk of galling or seizing of bolt and insert
  • Similar to NASM1130 inserts

Benefits of the Spiralock wire thread insert:

  • Provides proven superior vibration resistance to standard locking inserts
  • Duplicates a Spiralock® tapped hole
  • Combines the advantages of wire inserts with the vibration resistance and load distribution of Spiralock

Advantages of the Spiralock Drive Notch (DN®) insert:

Spiralock Drive Notch

  • Speeds installation and reduces labor costs due to elimination of breaking off tangs, their retrieval, and accounting for them
  • Eliminates the potential of foreign object damage (FOD-free design) or short-circuiting of electronics by loose tangs
  • Prevents harm to expensive castings by invasive tang removal techniques
  • Eliminates messy and environmentally unfriendly chemicals or adhesives
  • Competitively priced as compared to conventional inserts

Performance & Features

Spiralock inserts are made of cold-rolled Type 304 stainless steel wire (AS7245), work-hardened to a tensile strength above 200,000 psi, having a hardness of Rc43-50. The finished surface (8-16 micro inches) is exceedingly smooth, virtually eliminating friction-induced thread erosion.

It is important to select the proper insert length in order to balance the bolt tensile strength against the shear strength of the parent material. The insert lengths are calculated numbers because the inserts cannot be measured in the free state. The lengths are multiples of the nominal thread size, or diameter, of the insert. Please see Table III for insert dimensions. Using the insert length selection table below, an insert length can be selected which will produce a thread system strong enough to fracture a bolt before it will strip or damage either the parent material or the insert.

Recommended Nominal Insert Lengths Based on Parent Material Versus Bolt Material Strengths

Unified

Shear Strength of Parent Material (KSI) Bolt Material Minimum Ultimate Tensile Strength (KSI)
54 75 96 108 125 132 160 180 220
10 2 2-1/2 3 - - - - - -
15 1-1/2 1-1/2 2 2-1/2 2-1/2 3 3 - -
20 1 1-1/2 1-1/2 2 2 2 2-1/2 3 3
25 1 1 1-1/2 1-1/2 1-1/2 2 2 2-1/2 2-1/2
30 1 1 1 1-1/2 1-1/2 1-1/2 2 2 2-1/2
40 1 1 1 1 1 1-1/2 1-1/2 1-1/2 2
50 1 1 1 1 1 1 1 1-1/2 1-1/2

Metric

Shear Strength of Parent Material MPa
(Alum., Mag., Steel)
Bolt Material Minimum Ultimate Tensile Strength MPa
300 400 500 600 800 1000 1200 1400
70 1-1/2 2 2-1/2 2-1/2 - - - -
100 1 1-1/2 1-1/2 2 2-1/2 3 - -
150 1 1 1-1/2 2 2 2 2-1/2 3
200 1 1 1 1 1-1/2 1-1/2 2 2-1/2
250 1 1 1 1 1 1-1/2 1-1/2 2
300 1 1 1 1 1 1-1/2 1-1/2 1-1/2
350 1 1 1 1 1 1 1-1/2 1-1/2

 

The resilient characteristics of each coil in the Spiralock insert allows it to adjust independently to secure the maximum surface contact with individual threads in the parent material. As a result, loads are distributed more evenly. Each coil can flex independently to contact the greatest amount of parent material thread surface. Stress and fatigue concentrations are reduced to maximize thread strength and increase the reliability and life of the fastening system. Once installed, the outward spring-like force of the coils holds the insert into place. Furthermore, when the bolt is screwed into the insert and torque is applied, the crests of the bolt will push radially outward on the 30° ramp of the insert’s Spiralock thread form. The insert will transfer the energy outward into the parent material thereby locking the insert into the material.