Originally Posted By: ironraven
I've seen plywood break under jacks. I'm looking for a nice, low cost piece of 2'x1', quarter inch plate.

If there are any scaffolding companies around you check if they have any extra pieces of scaffold mudsill (jack pad). These are usually damaged laminated scaffold planks cut into 2 foot lengths.
They go under the scaffold legs to spread the load,
You will never push a jack through one and the jack is far less likely to slip than on steel.
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