This is a special stud used on 1964 260 and 289 Mustang engines with Eaton power steering pumps, and I assume other Fords, Mercurys, and trucks with a 221, 260 or 289 with Eaton power steering pumps for the pump belt adjusting bracket.
It is 4 35/64 inches long overall with a 1/2 hex drive with a flange located partway in the center. The threads are 5/16-18 X 3/4 in and 5/16-18 X 3 1/2 in (the hex flange is to the long side). The stud replaces a 379861-S8 bolt, 5/16-18 X 3 5/8 hex head place bolt in the water pump that goes thru the timing cover into the engine block. It's the 4th bolt clockwise from the top on the water pump. To complete the assembly of the adjusting bracket, two flat washers, 378288-S8 (one on each side of the bracket), a lock washer, 34806-S8, and nut, 33797-S8 are required. Ref 64-65 Mustang Chassis Assembly manual, AM0005 page 47, Mustang and Ford Small block, page 3-53. 3K2(d); page7-58 4K8(g).
In other words, if you find one, don't throw it away.
Jim
