The VFC 40mm Grenade Cartridges have quite a misleading name. This item while looking like an egg holder that comes with your eggs in the supermarket is actually a pouch insert. This Cold War-era repo gear is period correct, designed to fit in pouches, turning one of your pouches into a grenade pouch that can hold standard 40mm airsoft grenades and moscrats.

VFC 40mm Grenade Cartridges Holster (Olive Drab)
Polymer Construction Airsoft Cartridges Holster
Designed for wargames and decoration purposes
Triple grenade holder /carrier insert (for bandolier, ammo pouch) for 40mm AIRSOFT grenade