Help with crossword clue derivation

[Peregrina]

I can get the answer but can't see how the clue works.

"Single item can bend backwards" and the answer is Unit. Which I got, but I got there treating it as a simple Quick crossword answer. Can bend backwards seems redundant.

Can bend = tin U backwards. I think

Unit backwards = Tin (can) U (bend)?

Oh dear, seems obvious now! Thanks.

Could someone also enlighten me as to why Turn trade without a penny gives the answer Spell.
Trade - sell
penny - p but that should surely be with a penny?
And what's the turn doing there?

I am new to this cryptic business.

The definition is "turn" in the meaning of "take a turn", "have a spell" (e.g. in prison), I think - bit of a stretch if you ask me

"Trade" = sell, as you said, and "without a penny" means "outside of a P" so the word "sell" wraps around the P.

Thanks. I agree it seems a bit forced. I must remember - without can mean outside. We have a place locally called St Helen's without. Like there is a Green hill far away without a city wall, doesn't mean the green hill or St Helen's lacks a wall, it means it's outside the town wall.

They do get easier e.g. the French can be telling you to add le,