Wikipedia
Thunder-B (Airsoft grenade)
A Thunder-B distraction device is a simulation grenade formerly manufactured by Hakkotsu and now manufactured by Valken Tactical under the name "Thunder-V". It consists of a disposable plastic shell and a mechanism for causing the shell to burst open with a loud noise. It is commonly used in the sport of Airsoft, as a distraction device similar to a flashbang grenade or as a simulated area-of-effect weapon.