Nintendo test cards (FIFI's)

Back in The Day, I used to work for a company that translated PC video game titles into Playstation and N64.

To system test N64 games we’d transfer the programme onto ROM chips, which were then plugged into the sockets of what was essentially an oversized Nintendo cartridge chassis, which we could then just screw back together and plug into a normal N64 console. Around the office these were generally known as “FIFI’s”.

I can’t for the life of me find any mention of these on the web. Anybody know what “FIFI” might stand for? They were big, blue, and held together with big standard screws.