What do the different needle plates do?

The needle plate is the metal plate under the presser foot, and the shape of the hole in it changes what the machine does well.

The standard zigzag plate has a wide slot, because the needle has to swing from side to side. That slot is what allows zigzag, buttonholes and decorative stitches. Its drawback is that fine or soft fabric can be pushed down into the opening by the needle, which is why so many seams misbehave in the first centimetre.

A straight-stitch plate has a small round hole. It supports the fabric right up against the needle, so nothing gets pushed down. On fine fabric the improvement is immediate: fewer puckers, no fabric disappearing into the machine, and a visibly cleaner stitch. It also helps free-motion work.

The obvious hazard. Sew a zigzag with a straight-stitch plate fitted and the needle hits metal and breaks. Many computerised machines detect the plate and refuse the stitch. Mechanical machines do not, so it is on you to remember.

Some plates carry etched guide lines at set distances from the needle for seam allowances, and some machines offer a plate with a wider opening for particular applications.

Two maintenance points. A burr or scratch around the needle hole shreds thread and looks exactly like a tension fault — run a fingernail round it if thread is fraying for no reason. And the plate comes off for cleaning: it is the access to the feed dogs and the race, and that is where lint packs.

Fitting a straight-stitch plate to an ordinary machine is one of the cheapest real improvements available.