SCREW is an all-purpose name for a ship’s propeller AFAIK: as for the CHIPS debate, I’m not too sure. I’ve certainly done this gag using ‘Mr. Chips’ with a loud question-mark to follow (it was something like ‘Fish to join Mr. Chips?’), but you can see how ‘chippy’ might easily get shortened down to ‘chips’ on a building-site.

In addition to several dead horses being exhumed and flogged one more time (TEENAGER, CARPENTER, ERROR, SCHOONER), we also have – as you highlight – some downright peculiar surfaces and the duplication of SMALL in 5d. In fact, I did start to wonder whether this was actually a computer-generated puzzle! Apologies for the rant; I’ll endeavour to get out of bed on the right side tomorrow.

Incidentally, I believe that CAT (in jazz terms) is an abbreviation of the original HEP CAT. It’s somewhat dated these days but, for younger viewers, the quintessential hep cat would be Mr “Hello, and welcome to Jazz Club…..Mmmmm Nice” from The Fast Show.