Fremco 18 mm cleaning sponges, part 103-2018060, are packed 50 per pack and priced per pack for lightweight MiniFlow-class microduct work. At 18 mm the sponge proofs small microduct, clearing moisture and debris and confirming the path is open before fiber is jetted. Microduct is unforgiving of obstructions, so crews often send multiple sponges through a run, which is why they ship in 50-count packs. A high-consumption item on FTTH microduct builds. Millennium part #537907.