The unique bi-lateral expansion of Watt-Flex cartridge heaters eliminates the need for tight fits and makes them well-suited for use in oversized bores where conventional cartridge heaters cannot be used effectively.

Cartridge heater fit is measured as the difference between the inside diameter (I.D.) of the bore and the outside dimension (O.D.) of the heater.

The suggested fit for a Watt-Flex Cartridge heater is .010″ greater than the nominal Watt-Flex heater sheath diameter,.

For example, the ideal bore diameter is 1/2″ diameter Watt-Flex heater (0.495″ normal) would be o.502 –> 0.505″. At the maximum tolerance dimension of the heater (0.497″) and the minimum bore diameter, the heater would have a 0.005″ fit, allowing ease of insertion and removal.

Generally, smaller diameter heaters benefit from a tighter fit and fit can be loosened for larger diameter.