These are old plastic thimbles. I love the colours. Some of them are slightly the worse for wear, having spent some time embedded in a very strange piece of work I did for my Foundation course a few years ago. Here's a detail -- just a detail as the full thing was too strange for mortal eye to behold.
You can see some of the thimbles cowering under layers of wax and glue. Happily I rescued the thimbles when I decided to break this monster up.