SAE Flare Nut Socket Set 7-Piece, 3/8 In Drive, 3/8-3/4 In

This is the Lisle 13180 set: seven flare nut sockets in 3/8, 7/16, 1/2, 9/16, 5/8, 11/16 and 3/4 in., all on a 3/8 in. square drive. A flare nut socket is a six-point socket with a slot cut through one side so it slides over the line and then grips five or six flats of the fitting instead of the two flats an open-end wrench catches. That is the difference between backing a cooler line nut off and twisting the corners off it.

The job this earns its keep on is the transmission cooler line at the case and at the radiator. Those nuts sit in road salt and heat for a decade, and the steel is soft. Once you round one you are cutting the line and splicing it. Because these are sockets rather than wrenches, you can put a ratchet or a torque wrench behind them and pull in a straight line instead of levering sideways on a fitting you cannot see.

The same sizes cover brake lines, master cylinder fittings, power steering high-pressure fittings, and the wired temperature sensors and thermo switches where a regular deep socket will not clear the pigtail - the slot in the socket wall lets the wire pass through. Chrome finish, 3/8 in. drive throughout, limited lifetime warranty from Lisle.