I am trying to make the following effects in sketch. As presented in the picture, they seem to have a curved and border radius cut to their ends.
To create arc we need Scissors tool.
In that way you can create any arcs, combine them and get desired result.
You can download sketch file here
Sketch is a bit primitive, all jokes and puns aside.
The easiest way, make an arc, give it the width you want, then place a small circle at each end, in the same size as your width. Cheating, but... well, pretty much everything is a cheat, in graphics.