With a Viscosity Regulated Bypass; which regulates a valve with similar oil temperature control effects as a thermostat. Offset design is required when installing an oil cooler on any TCA (Dyna; Touring) or TCB (Softail) Twin Cam model. It is optional for cooler installation on all fuel injected Evo Big Twins with engine mounted spin-on oil filters for easy access to oil lines. Adapter allows the oil to flow through the filter before entering the cooler; resulting in less restriction. After filtration; the oil will by-pass the oil cooler automatically while the engine warms up to standard operating temperature. Once the bike reaches operating temperature; the Viscosity Regulated Bypass closes the by-pass hole completely and the sends 100% of the hot and filtered oil to the oil cooler; and delivering cooler; clean oil to the engine. Oil flow direction from adapter: oil feeds the oil cooler from the fitting on the left side and returns to the fitting on the right side; as viewed from front with oil filter adapter fittings at bottom. Note: See 970706 for replacement thermostat with gasket service kit and 970727 for the gasket service kit only.