This kit replaces parts #29, #30 and #31 in your KJW KC-02. The bolt stop, the bolt stop spring and the small pivot pin.
The new bolt stop is custom-designed by RogueWorx and made from a stainless steel. This makes it much stronger than the standard bolt stop which is made of weak pot metal which is prone to bending and snapping.
This is considered to be a standard essential upgrade.
Installation video here: https://youtu.be/evz-h8Lu9Ls