This is a 3D Printable In-Line Fuse. It works by you inserting two wires 14-16 Gauge that have all-metal female spade connectors on the ends that will go into the plastic fuse housing. You can then use a soldering iron set to a high temperature inserted into the round part of the female spade connector to heat it up to allow it to fit in snugly into the plastic housing, very similar to a heated insert. let it cool off fully before using, and it's recommended to use a higher temp rated filament for the housing; Atleast PETG.