The 408 models of speed/temperature sensors feature removable modules to allow cleaning and inspection of the paddlewheel. A blank plug is provided to insert into the hull fitting during this operation. The module and plug have dual O-ring seals and are secured into the hull fitting with a stainless steel pin and ring. An extra safety feature on Model 408P is a length of stainless steel chain to hold the module in place should it receive a blow from the outside.
Model 408P hull fitting and module is made of glass filled nylon. Model 408B has a bronze thru-hull fitting. (Shown at the right).