Q: We are essentially having issue identifying the highest available high strength stainless steel nylon insert nuts. Is Duplex 2205 the best option?

A: If you are just looking for strength for your lock nut with a nylon insert, one of the highest strength stainless steel’s you could consider would be 17-4 PH (ranging from 136-190KSI)

A286 locknuts are a good option as well with good high temperature stability (130 KSI)

Duplex lock nuts are also much stronger than 316 with about 120KSI tensile strength. Duplex also offers better corrosion resistance. This material is not as strong as A286 or 17-4

I am bolting 321 stainless steel ducts (we are discussing changing to grade 91 alloy but this is only a possibility), and want to use locknuts to minimize potential for debris. The application is at 900-1050F at the bolts, so I am not sure what locknuts are available at this temperature.

I was thinking of A193 grade B8M bolts but am open to suggestions if there is a reason to use another bolt spec that is suitable for this temperature.

A: For a high temperature application like this you might want to consider an A286 Lock Nut in the Flexlock style. This is an all metal lock nut and is very oxidation resistant and has great high temperature stability when compared to B8M. A286 is usable to about 1300F which is well within your temperature needs.