Turn a bolt into each one about a inch and half long at the least , longer is fine and just cut them down to length , you will need at least 3/4 of thread from the mushroom bolt to be able to screw into place, longer is fine, make sure you apply copper slip to the threads to act as a extra seal and protection from rust so they do not fuse into place, if you were close by i would sort these quick for you.
M-m
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