This is a small buffer piece that goes between the recoil spring and carrier in your Mod9v2. Proven to reduce damage to carrier fin caused by the spring. So far tested at 500+ rounds rapid / double tap. Carrier showed no signs of stress or damage after testing.
This is intended for the 1.4mm WD x 12mm OD x 300mm long / McMaster part# 9637K83 spring that is recommended by Derwood in the latest Mod9v2 Odysee upload.