Speed nocks are brass clips that would be clamped on the string and then a piece of shrink tube would be put over the top. Sold individually and come with black shrink tubing.
When purchasing speed nocks make sure you count all the nocks under the shrink wrap by counting the bumps, this goes for top and bottom of the string. Some bows may only require 2 on the string 1 on top and 1 on the bottom while others may require 32 nocks, 16 on the bottom and 16 on the top. The amount you purchase is the amount you will receive or installed on your string.