Fifty {Two} Shades of Grey - Week 38

These items are from way back in my history... more than a few years... more years than I really care to admit to.
Most people will probably struggle to identify correctly what they are, because they are really not an item you would usually come across.
I will tell you they come in sets of four pieces.
There are two different items and two of each item in each set.
They are made from pressed metal (I think).
And these particular items were made in the South Island of New Zealand.

Any the wiser??
These are heel tap plates which are screwed onto tap dancing shoes used by tap dancers.
Why do I have them I hear you ask...?
I used to dance competitively and taught tap dancing for a number of years. As a tap dancing teacher, I had them on my tap shoes, so my dance students could not only see the steps but hear all the tap beats that they should be making while doing the steps.