I believe that this particular one is one of the larger, perhaps 1mm diameter or a bit more, for this Pentax lens.
In the future, when removing that aperture ring, do so in a clear food storage bag so that nothing goes flying.
Nota Bene for all: for literally more than a decade I have been saving tiny screws, ball bearings, tiny springs, etc, that I have garnered though junk bodies and lenses that I am not able to fix. I save these precious tiny parts in small, plastic coin rolls that have a screw on cap. This is probably the most valuable source of parts that I have and I recommend that, before you through anything out, you scavange these tiny parts. They WILL save your day. - David Lyga
Great advice, David. I always do the same.
I do use a digital device in my photographic pursuits when necessary.
When someone rags on me for using film, I use a middle digit, upraised.