Threadlocker Guide: Loctite Colours, Strengths and When to Use Each

Bolts on pumps, gearboxes, motors and presses loosen because of vibration, and a loose bolt is a common cause of stoppages and repeat repairs. A threadlocker is a liquid that cures inside the thread and stops that loosening. This guide explains the threadlocker colors used by Loctite, what each strength class means, and how to choose the right grade for your fasteners. Every strength class, colour and size limit below is taken from the Henkel Loctite technical data sheets listed at the end.

What a threadlocker does and why bolts loosen

Henkel's data sheets describe these products as one-component, anaerobic adhesives. They stay liquid in the bottle, where air is present, and cure when confined between close-fitting metal surfaces with no air. In a bolted joint, that means the liquid hardens in the gaps of the thread and fills them. The cured product locks the thread and also seals it, so it prevents loosening and leakage from shock and vibration.

A tightened nut is held only by friction, and vibration can overcome that friction in small steps. Filling the thread with a cured adhesive removes the free movement, so the nut stays where it was tightened.

Threadlocker colors: what purple, blue, red and green mean

Loctite uses colour to tell the grades apart, and the colour you see is the colour of the uncured liquid. The strength class is printed on each data sheet.

Because the colour is only the liquid's appearance, always confirm the grade number on the bottle. Two products with the same colour can differ in viscosity, strength and the surfaces they are meant for.

Loctite grades compared: 222, 242, 243, 262, 271 and 290

Thixotropic means the liquid stays where you put it, so it does not run off the thread after application.

Which blue grade: Loctite 242 or Loctite 243?

Both grades are medium-strength and meant for joints you will open again with standard hand tools. According to the April 2025 data sheet, Loctite 243 offers high temperature performance and oil tolerance, tolerating minor surface contamination from cutting, lubrication, anti-corrosion and protection fluids. It works on active metals such as brass and copper, and on passive surfaces such as stainless steel and plated parts. The data sheet names pumps, gearboxes, motors and vehicles as typical equipment.

On a maintenance floor, where parts are rarely perfectly clean, that oil tolerance is a practical reason to prefer 243 for everyday machine bolts.

How to choose: strength, size and whether you will open the joint again

Work through these questions in order.

1. Will you need to open the joint with hand tools? If yes, choose purple (low strength) or blue (medium strength). Red grades are for permanent locking.
2. How big is the fastener? Purple 222 suits small screws. Red 262 and 271 are described for large bolts and studs up to M25.
3. Is the part already assembled? Choose green 290, which wicks into the thread by capillary action, so you do not need to take the joint apart first.
4. What is the surface like? The rate of cure depends on the metal. Loctite 243 is described for both active metals (brass, copper) and passive ones (stainless steel, plated surfaces), and an activator can speed the cure where it is too slow.
5. Is the surface oily? Clean it first. If you cannot clean it fully, check that the grade tolerates oil, as Loctite 243 does for minor contamination.

Selection checklist

• Joint must be opened again with hand tools: purple or blue
• Large bolts or studs that should stay put: red
• Already assembled, and the thread cannot be taken apart: green
• Machine bolts with light oil on them: Loctite 243
• Small set screws and fine threads: Loctite 222

Surface preparation and cure time

The Loctite 243 data sheet gives these steps for assembly:

1. Clean all surfaces, external and internal, with a Loctite cleaning solvent and let them dry.
2. If the cure speed is too slow, use an appropriate activator and let it dry.
3. Shake the product well before use.
4. Keep the nozzle tip away from metal surfaces, so the product does not clog it.
5. On a through hole, apply several drops to the bolt at the nut engagement area. On a blind hole, apply several drops to the lower third of the internal threads, or to the bottom of the hole.
6. Assemble and tighten as required.

How fast a threadlocker cures depends on the metal, the gap in the thread, the temperature and whether an activator is used. The data sheets show these effects as graphs, and the strength figures they publish are measured after 24 hours at 23 °C. Plan on leaving a joint to cure before you put it under full load, and read the cure graph for your grade and surface.

Common mistakes

• Using red where you will need to service the joint. The data sheets for 262 and 271 describe permanent locking. The data sheets give localised heat of about 250 °C as the way to open a joint when hand tools do not work.
• Skipping the cleaning step. The data sheet advises cleaning all surfaces with a Loctite cleaning solvent before assembly. Oil tolerance covers minor contamination only.
• Putting the wrong grade on a small fastener. Purple 222 is described for set screws and small fasteners, where easy removal is needed without shearing the screw.
• Loading the joint too early. The published strength is a 24-hour value at 23 °C, and the data sheets say the rate of cure depends on the temperature and the substrate.
• Letting the nozzle touch the metal. The data sheet warns that it can clog the tip.

Where to buy genuine Loctite in Delhi NCR

Multiweld Engineering is an authorised distributor of Loctite for Delhi NCR. See our full range of Loctite products in Delhi NCR, or read more on the Loctite brand page. Our warehouse is at Kherki Daula in Gurgaon, close to the industrial town of Manesar, and we supply factories across the National Capital Region.

Tell us the grade, the bolt size and the quantity, and we will confirm the right product. You can contact us for a quote.

Sources and references

• Loctite 222 technical data sheet (Henkel, May 2022)
• Loctite 242 technical data sheet (Henkel, February 2022)
• Loctite 243 technical data sheet (Henkel, April 2025)
• Loctite 262 technical data sheet (Henkel, February 2022)
• Loctite 271 technical data sheet (Henkel, March 2012 edition)
• Loctite 290 technical data sheet (Henkel, February 2022)

Data sheets are revised from time to time, so check the current edition on Henkel's site before you specify a grade.