"PM-28 EARTH CRYSTAL" is a Item for Transformers EARTH WARS.
The peg and hole of crystal is 5mm.So,Your figure may have crystal.
PEACE_MAKER_DDMTF create your TF weapons and items:)
Blog:http://ddmtf.blog.fc2.com/
twitter:https://twitter.com/hoshihane_sui
Thank you.