Thread locker and torque: does Loctite change the torque spec?
Tighten a bolt with LOCTITE 242 to its normal dry torque: Henkel rates the product's effect on the nut factor at −10% to +10%. For 243, 262 and 271 Henkel publishes no lubricity figure at all, so there is no sourced basis for a reduction. Apply it wet, assemble, and torque as specified.
Contents9 sections
Key takeaways
- LOCTITE 242 lubricity, ASTM D5648: K changes by −10% to +10% on 3/8-16 phosphate-and-oil hardware 1.
- Henkel adds that in critical applications 'it is necessary to determine the K values independently' 1.
- No K or lubricity value is published for LOCTITE 243, 262 or 271 2 3 4.
- Breakaway torque on the data sheet is the adhesive's strength on unseated bolts, not a tightening torque.
- 262 and 271 are permanent: Henkel's disassembly instruction is localized heat to about 250 °C 3 4.
Quick facts
| LOCTITE 242 K change | −10% to +10% 1 |
|---|---|
| LOCTITE 243, 262, 271 | No K published |
| 242 / 243 removal | Standard hand tools 1 2 |
| 262 / 271 removal | Heat to about 250 °C 3 4 |
The short answer
A liquid thread locker goes on wet and cures after assembly, so during tightening it sits in the threads like a thin fluid. Whether that changes the torque needed for a given clamp load is a question of the nut factor K in T = K × D × F 5. Henkel answers it for one product only.
The LOCTITE 242 data sheet lists “Lubricity, ASTM D5648, K value, %” as −10 to 10, tested on 3/8-16 phosphate and oil nuts, bolts and steel washers 1. In other words, K with 242 stays within ±10% of the reference hardware without it. That is inside the normal scatter of torque tightening, about ±25% with a torque wrench 6, so the dry torque stands.
Henkel qualifies the number: “In critical applications, it is necessary to determine the K values independently. Henkel Corporation makes no warranty of specific performance on any individual fastener” 1.
For LOCTITE 243, 262 and 271, the current data sheets give breakaway and prevail torques and cure data but no lubricity or K value 2 3 4. Any percentage you see quoted for them did not come from Henkel’s data sheets.
What ±10% means on a real bolt
Take a 3/8-16 Grade 5 bolt at 75% of proof load: 31 ft-lb (42 N·m) plain dry for about 4,940 lbf, from the bolt torque calculator. If LOCTITE 242 moves K from 0.20 to anywhere between 0.18 and 0.22, the same 31 ft-lb gives:
| K | Clamp load | vs. dry |
|---|---|---|
| 0.18 (−10%) | 5,510 lbf | +11% |
| 0.20 (dry) | 4,960 lbf | – |
| 0.22 (+10%) | 4,510 lbf | −9% |
Even at the low-K end, the bolt sits at about 84% of its 6,590 lbf proof load. Compare oil (K 0.15) at the same torque: 6,610 lbf, a third more than intended and just over proof load.
Thread locker and lubricant together
If a joint is also oiled or anti-seized, the lubricant sets K and the locker is a minor change on top. Henkel’s directions start by cleaning all surfaces with a LOCTITE cleaning solvent and letting them dry 1. On clean threads, use the dry torque. LOCTITE 243 is described as tolerating minor surface contamination from oils such as cutting, lubrication and protection fluids 2, but that is about cure, not about K.
Don’t apply a lubricated-thread reduction because a thread locker is present. It is not a lubricant in Henkel’s data, and the lubricity figure for 242 says so.
Breakaway torque is not tightening torque
Data sheets list strength numbers that look like torque specs. They are not.
| Product | Test fastener | Breakaway torque |
|---|---|---|
| 242 | 3/8-16 steel nuts (Grade 2) and bolts (Grade 5) | 70 to 150 in-lb (7.9 to 17 N·m) 1 |
| 243 | 3/8-16 steel nuts and bolts, unseated | 110 in-lb (12 N·m) 2 |
| 243 | M10 black oxide bolts, mild steel nuts, unseated | 200 in-lb (22 N·m) 2 |
| 262 | M10 steel nuts and bolts | 190 in-lb (22 N·m) 3 |
These measure how hard the cured adhesive holds a nut that carries no preload. The 3/8-16 Grade 5 bolt above is tightened to 31 ft-lb, which is 372 in-lb. The adhesive’s job is to stop that preload from being lost to vibration, not to replace it. Henkel describes 242 and 243 as preventing loosening and leakage from shock and vibration 1 2.
How to apply it
From the LOCTITE 242 directions for use 1:
Clean
Clean all surfaces, external and internal, with a LOCTITE cleaning solvent and let them dry.
Activate if needed
On inactive metals or if cure is too slow, spray the threads with activator and let it dry.
Through holes
Apply several drops onto the bolt at the nut engagement area.
Blind holes
Apply several drops down the internal threads to the bottom of the hole.
Assemble and tighten as required
That is, to the specified torque.
Cure depends on the metal and the temperature. Henkel’s 242 curves show strength building over 24 hours on M10 steel, slower on stainless and zinc dichromate and slower when cold 1.
Taking it apart
| Product | Strength | Disassembly |
|---|---|---|
| 242 | Medium | Standard hand tools 1 |
| 243 | Medium | Standard hand tools; in rare cases with long engagement, localized heat to about 250 °C 2 |
| 262 | Medium to high, permanent | Localized heat to about 250 °C, disassemble hot 3 |
| 271 | High, permanent | Localized heat to about 250 °C, disassemble hot 4 |
Henkel lists 262 and 271 for large bolts and studs up to M25 3 4.
Common mistakes
- Cutting torque “because of the Loctite”. For 242 the data says K moves no more than 10%. For the others there is no published basis for any cut.
- Torquing after the locker has started to cure. Assemble and tighten while it is still wet. Re-torquing a cured joint reads the adhesive’s breakaway strength along with the bolt’s friction.
- Using a locker on a torque-to-yield bolt without the procedure calling for it. Follow the service information. See torque-to-yield bolts.
- Reading breakaway torque as the install spec. See the table above: it is a fraction of the tightening torque.
- Skipping the clean step. Henkel’s first instruction is to clean and dry the surfaces 1.
Sources
- 1Henkel Corporation (LOCTITE), LOCTITE 242 threadlocker TDS, February 2022Checked 21 Oct 2026
- 2
- 3
- 4
- 5
- 6
Spotted a value that doesn’t match its source? Report an error
Related
- Dry vs lubricated torqueWhy oiled bolts need less torque than dry ones for the same clamp load, with nut factor K values from Fastenal, NASA and Henkel for oil, zinc, anti-seize and moly.
- Anti-seize torqueHow much to cut torque with anti-seize, from LOCTITE data sheets: copper and metal-free K 0.16, marine and silver 0.18, moly 0.11. And why NGK says no on plugs.
- Lubricated torqueConvert a dry torque spec to oiled, zinc, anti-seize or moly threads by the ratio of nut factors. 100 ft-lb dry becomes 80 ft-lb with copper anti-seize.
- Bolt torque calculatorBolt torque calculator for SAE and metric bolts by size, thread, grade and lubrication, using T = K × D × F with the proof loads from SAE J429 and ISO 898-1.