I have a plate of aluminum 5 mm thick to which I would like to attach a hook. The plate runs roughly vertically, but only spans around 18 cm from anchor point to anchor point. The hook should be able to withstand upwards of 1000 kg.
I've drilled a 12 mm hole through the plate and my strategy is to insert the hook bolt in it and tighten it using a nut on each side.
However, in order to keep the aluminum from deforming, I'm going to need one or two steel washers.
My question is, whether it is necessary to use a washer on both sides or whether one side is sufficient?
If one is enough, does it make any difference, which side it rests on?
My reasoning goes like this: The job of the washer is to keep the hook from bending the aluminum by spreading the force over a large area. As long as a single washer is taut against the aluminum – held there by the nut – the hook won't be able to bend either way.