Can anyone tell me what these are?

[BillTodd]

That's the bit I'm calling the large part (large=wide) :)

Some further thoughts:(in random order)

I believe/guess the aluminium casting dates this to mid 20thC - probably post WWII.

The long cylinder is screwed to the central casting meaning it was not easy to remove. Since the ratchet clearly pulls towards to the larger part, it would have been difficult to thread the whatever between the rollers - suggesting that once set-up the unit was not disturbed too often.

So, I wonder if it is somekind of tensioning device ?

In what part of the UK was it found? (e.g. Lancashire might suggest spinning or weaving use, South coast rope making etc. )

Were there just the three of them?