I actually designed it to clean up and organize the the duramax return system....you know all those hard lines we love that run all over the valley of the engine. With this block you can now use A/N fittings along with stainless steel hose to clean it all up and give everything a professional stylish look. Its meant for the 2 return lines of the heads, 2 returns of the 2 CP3 pumps, 1return of the high pressure block, and the fuel temperature sensor in the return system will actually fit in any port of the block, then 2 ports left one for the return to the tank and an extra for a guage or whatever the case may be.