The color of an anaerobic threadlocker is not decoration. Across the industry it signals a strength class and an intended use, and for a manufacturer specifying hardware, reading that code correctly is the difference between a joint that stays put and one that either backs out or cannot be serviced.

The Color System and What Each Grade Does

Exact formulations vary between suppliers, but the color convention is consistent enough to design around.

Purple, low strength. For small fasteners, roughly M6 and below, that need frequent adjustment. Low breakaway torque, removable by hand. Common on set screws, adjustment screws, and small electronics hardware.

Blue, medium strength. The general-purpose grade. Solid resistance to vibration and shock, still removable with hand tools at a higher-than-normal breakaway torque, no heat needed. Used across machine building, automotive, and equipment assembly where periodic service is expected.

Green, wicking and retaining grades. Low-viscosity wicking grades penetrate threads on already-assembled parts such as set screws and instrumentation hardware; they typically fall in the medium-to-high range. Green retaining compounds for bearings and cylindrical fits are usually high strength. Removal depends on the specific product, so check the data sheet.

Red, high strength. The highest standard color class. Formulated for permanent joints where maximum resistance to vibration, shock, and harsh conditions is required and disassembly is expected only at major overhaul. Highest breakaway and prevailing torque. Removal requires localized heat, roughly 250 to 300 degrees Celsius at the joint, then hand tools. Attempting to remove red without heat risks stripped threads and sheared fasteners.

Why Red Holds Hardest

Red grades cure into a denser, more highly cross-linked polymer network than lower grades. Confined in the thread path, that rigid network strongly resists the rotational forces that drive self-loosening. The same rigidity is why heat is the removal route: the polymer softens and loses adhesive grip at elevated temperature. “Permanent” here means “needs a defined method to remove,” not “impossible to remove.” That distinction belongs in every service manual.

The way a rigid bond behaves under cyclic and thermal load connects to how CTE mismatch causes adhesive bond failure, where stiffness and differential movement interact.

Specifying by Color, Correctly

• Match strength to disassembly need, not to a preference for “more secure.” Red on a fastener that will need routine service creates damage and downtime. Blue on a joint that must never loosen risks a field failure.
• Account for substrate. Passive metals such as stainless and aluminum slow cure and reduce ultimate strength regardless of color; plan for an activator.
• Check temperature rating. Standard grades cover common industrial ranges; sustained high heat needs a grade qualified for it. For joints that run genuinely hot, our guide to high-emissive ceramic coatings by service temperature covers the wider thermal picture.
• Read the data sheet for the exact product. Shear strength, breakaway and prevailing torque, temperature range, cure times, and removal instructions vary within a color class between product lines.

If you are choosing a strength class for a critical fastener and want the selection checked against your load and service profile, Email Us with the fastener size, substrate, and expected maintenance interval.

Strength Ratings Are Not Directly Comparable Across Colors

A data sheet quotes breakaway torque and prevailing torque, usually measured on a specific fastener size on grit-blasted steel. Those test conditions are rarely your production conditions. A red grade rated far above a blue grade on M10 steel may show a much smaller advantage on plated M6 hardware, and on passive stainless the gap can nearly disappear without an activator. Fastener size also matters: the same grade produces different breakaway torque on a small screw than on a large bolt because engagement area scales with thread diameter and length. When comparing options, normalize to your own fastener, substrate, and surface finish rather than trusting the headline numbers. The practical selection question is almost never “which color is strongest” but “which grade gives enough retention for this load while still allowing the disassembly this joint will actually need.”

Practical Notes for Production

Record the specified color and grade against each critical fastener on the drawing and in service documentation, so maintenance uses the correct removal method. Keep the different grades in clearly separated, labeled dispensing stations to prevent a high-strength grade going onto a serviceable joint by mistake. During process qualification, verify breakaway and prevailing torque on sample joints built from production hardware, and re-verify whenever the fastener finish or supplier changes. The reversibility question, permanent versus serviceable, is the same trade-off weighed in our comparison of UV adhesive and epoxy for heavy-duty repairs.

Used correctly, the color code is a fast, reliable shorthand for strength class. Used carelessly, it produces joints that are either under-secured or impossible to service without damage.

Work With Incure on Threadlocker Specification

Incure is an industrial adhesives manufacturer that helps engineering teams select an anaerobic threadlocking grade for the substrate, gap, and service conditions, and document the surface prep, activator use, and removal method that go with it. Contact Our Team to review your fastener specification.

Visit www.incurelab.com for more information.