What's better for installing aluminum mast steps: rivets or tapped threads?

[a64pilot]

Originally Posted by bobgarrett

Why use steel screws?

.

Shear strength.

[bobgarrett]

Originally Posted by john61ct

I am in love with rivnuts.

Doubt they come in aluminum, but for SS check out the plusnuts variety.

Don't buy cheap from sources not tied to the real mfg.

But they do...
https://www.spaldingfasteners.co.uk/...-m5-m6-m8-m10/

[john61ct]

Sorry my syntax was not clear.

I doubt the Plusnuts variant comes in aluminium.

[Toaster]

Originally Posted by a64pilot

Shear strength.

The lowest couple of mast steps make very nice hand holds in rough seas, which means you end up swinging on them and applying quite large sideways torques - resulting in loose steps due to deformed rivets simply because Al rivets are not strong enough. Therefore, I use 1/4-20 SS machine screws on those two steps (with Tefgel), they are still tight after a few years. Rest are Al rivets and still tight after 40 years.

[bobgarrett]

I am no expert but whether using steel or not, the mast it is fastened to is aluminium.
According to one web site the UTS of their aluminium is 505MPa but for steel 570MPa. Of course different grades will differ. Shear strength factors against these are also fairly similar.
Now these numbers are not as different as I would expect so maybe some expert will come on and clarify.

[Suijin]

One warning related to aluminum steps: be very careful about any lateral stresses on them, such as when the mast is down on saw horses or if a line gets wrapped around one. They are fine for supporting your weight vertically but can bend sheer or weaken from lateral “injury”. Have seen a few fail from this kind of stress.

[N1EYO]

Google “Rivnuts”