(1) It seems to be the case that Milton's made this word up, this wonderful word scrannel.

(2) This last line that I've read seems itself to have been grated on a scrannel pipe.

(3) We have no idea what this menacing contraption actually is supposed to look like or what it's actually intended to signify, but we can know, I think, with some certainty that it's not scrannel.

(4) At least that's what the OED tells us; the only example that they can find of the word scrannel is in Milton's Lycidas.

(5) I have to read these lines again: "And when they list, their lean and flashy songs grate on their scrannel Pipes of wretched straw."