Spanish to English Tech/Engineering Agriculture Threshing

Hi, I would appreciate your help with a few technical terms regarding ploughing and farming implements.

The guide is from a village in Spain (Castilla La Mancha), so some terms/implements might be specifically from there, but an English equivalent will do perfectly.

They are part of a guide and there isn't much context except for a line or 2 as they are just short explanations.
It looks like a trestle missing the legs of one side but with the centre piece as the third "pie"

Context is:
"Los tres pies se colocaban por debajo de las ruedas de los carros y bajando la palanca se levantaban éstos y se retiraba la rueda para poder engrasar."

Thanks :)