This is a 4C type gas-pressurized refill. There are no other examples. It was produced as a refill for the Tombow Design Collection Outdoor Model, XPA, but it has been discontinued. I contacted the manufacturer and purchased all of their remaining stock. These are the last two remaining. If you install it in other 4C compatible models such as the Lamy 2000, you can use it as a gas-pressurized ballpoint pen. These are rare items that are no longer available, so please consider this opportunity.