This is the easy way to find air leaks in charged air cooling systems on class 7 and 8 trucks. Using the quick disconnect air fittings, the OTC-5039 connects right to a 3�, 3-1/2� or 4� cooler hose. The unit has a large 2-1/2�, 0 to 60 psi pressure gauge, regulator and relief valve and (2) safety cables.