This type of heaters is different from the flange-mounted heaters. They are much more compact and, normally, they are designed for lower heating power values. Nevertheless, the selection criteria, and those relevant to the operating conditions, are the same as those used for the flangemounted heaters. This ensures that also these products can be employed safely in classified areas. Their features make them suitable to heat directly or indirectly highly flammable substances (solvents) o highly explosive (GPL). Plug-mounted heaters are manufactured using threaded supports (plugs) made of brass and stainless steel. The heating elements are manufactured using electrowelded tubes made of stainless steel AISI316Ti, AISI 316L seamless and Incoloy 800. The terminal box is directly screwed on the plug which hosts the heating elements and is normally an aluminium-cast component. However, for applications in corrosive environments, a terminal box in AISI316 can be provided too. The electric terminal box has been designed divided into two separate shells, to facilitate the heater electrical connection operations. It can host inside the safety temperature sensor and, in many of the possible operational constructions also a second sensor edicated to the process control.