Z Irons were a pair of heavy pieces of steel bent in a "sort of " Z shape but with the ends on a 45 degree angle ..... if you had a situation where your hydraulic bottle jack could not fit into a small opening (like say a space case in a train incident as one example) you would place the pair of Z Irons in the small opening & put the bottle jack in the open end of the Z's & pump the jack & the spread would be transposed to the other lips of the Z's spreading the objective...thats just one example ...your imagination played a big part in their usefulness....we had a large & a small pair of them in R*2 & had them on the Rig until some newer power units basically eliminated the need & did the work more efficiently.....we did keep them as a backup until the Rig became super overloaded with newer equipment .....I remember an old WNYF article on them ...maybe someone can find & post that....one picture is worth a thousand words.