Stuffing box tubes lined with Teflon offer a superior, virtually frictionless, surface for shafts to spin freely when use with a good quality grease. Radio interference and the heat generated from contact points could anneal the shaft in that spot causing it to break when using just brass tubes. Racers know the RPM gains from using these tubes. 1/4" Tubes are 11/32 OD. 3/16" Tubes are 9/32". Teflon is permanently installed in tubes. DO NOT heat tubes with Teflon installed! Tubes come in 3 lengths - 12", 18", 24" and should be cut to length. One end is reduced to allow it to be installed in a nose piece or strut for support at the transom.