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Who makes these exhaust clamp bolts? (Socata TB20 exhaust clamps)

Interesting – many thanks. Are these some sort of high-temp stainless steel?

Curiously, Socata sells the 12-point nuts very cheaply, under €1 IIRC. But they corrode fast. The M6 nut at £3.22 is fine.

Also, because the Socata bolt has the blank section, the spacer is required.

I managed to buy 20 of the genuine Socata bolts, very cheaply, from the same source as these. So I have the “real” ones, as well as the ones above. I also got a load of the clamps but no extra ones for sale.

Shoreham EGKA, United Kingdom

here you have the spec of the K nuts please note on 2nd page 12 point nuts with higher temp range!!

Last Edited by Peter_Paul at 29 May 10:24

I can’t get the PDFs to load.

Shoreham EGKA, United Kingdom

try Hex nuts and double Hex nuts


Well I am damned… works in Firefox but not Chrome.

Curiously the hex nuts

don’t come in as wide a temp range as the double hex nuts

but there is a curious one there which looks like Inconel but with a very low temp rating… is that right?

The specified temp bears little relation to the material. I wonder why.

I am sure exhaust clamp bolts and nuts should be 600C at least; the exhaust is dull red hot which according to this is 600-700C.

Shoreham EGKA, United Kingdom

for sure they get hot !!


The fact it’s visibly red means the temperature is 400 Celsius or more, so 235 Celsius nuts are not correct

Darley Moor, Gamston (UK)

How can any stainless steel be ok for 235C and not ok for 400C?

If this is so, it does make one wonder about the bolt also – unless the nut issue is something unrelated e.g. the method of locking used.

Shoreham EGKA, United Kingdom

As the given operating temperature increases, the strength of the material decreases. For whatever reason, the table is just giving you one strength and temperature data point. Each alloy has their own properties which vary with temperature; strength, fatigue, creep…. If you know what alloy you have and what strength and temperature profiles are required, just get the real data sheet (see a sample chart below – doesn’t look exactly the same as the nut table, so the heat treatment might be different).

For the highlighted entry, at 235 degrees C the strength is 1800 MPa, whilst in the listing right above it (for 600 degrees C), the strength is 1550 MPa. If you can get a data sheet for this product, you can read of the value at 400 celcius. I don’t see that the 235 degrees Celsius is limiting (unless of course there is something else going on, e.g. the plating might not tolerate the heat, etc.).

Last Edited by Canuck at 29 May 18:21
Sans aircraft at the moment :-(, United Kingdom

just looked for EN2894 and EN4011and found the following

EN 2894

Aerospace series – Nuts, bihexagonal, self-locking, with counterbore, in heat resisting nickel base alloy, passivated, MoS2 lubricated – Classification: 1 550 MPa (at ambient temperature) / 315 °C

EN 4011
Aerospace series – Nuts, bihexagonal, self-locking, in heat resisting nickel base alloy NI-PH2601 (Inconel 718), silver plated – Classification: 1550 MPa (at ambient temperature)/600°C

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