As an excuse I claim that the difference is minuscule at check 0.03125mm... damn metal threaded screws just don't DWIM. It took me two extra trips to the hardware store to learn this crucial fact.

Whoever decided that Oz should use metric and imperial screw gauges in parallel should be sentenced to rethreading all the imperial ones to metric with a blunt kitchen knife.

All I wanted was to replace the {broken|lost|ugly|mismatched} cupboard door knobs I had successfully and stolidly ignored for about a year now. So I went to Bunnings (which is open until 2100 weekdays - perfect for the DIYist in need of a quick fix of his favourite drug) and bought 5 plastic globes packaged with screws. Screws looked ok, plastic packaging didn't mention a type so I assumed (Ass-You-Me) they were metric.

Well, in fact I didn't care about them being metric, martian or whatever - until I realised they were too short, by about 6mm. Nothing in my scrounge bag matched the required length. Sigh.

Next day: I measure an existing screw. Caliper says "about 4mm - give or take" which is not surprising given that the caliper is a cheap plastic POS, but I don't think even an expensive one would have helped me much. Note that I'm still not thinking "imperial?".

I visit another hardware shop, see a collection of metric screws in suitable lengths, buy them. In the evening I try them: no cookie, of course.

Carefully squinting at the screws side-by-side I finally realise my mistake. Second trip to the store, look for something not-quite-unlike-4mm in the small rack of imperial anachronisms, and voila.

Now I'm proud owner of a set of misleading imperial screws and matching nuts, ready to wreak havoc on any 4mm metric gear in the vicinity maniac cackle!