The Lisle Corporation 17mm and 21mm Line Sockets, No. 12490, are designed to replace 17mm and 21mm fuel line fittings without damage to fitting, fuel rail, and fuel line, reducing the possibility of fuel leaks. The 17mm socket works on Audi A1, A3, A4, A6, A8, Volkswagen Passat, and BMW N54, N63, and S63 engines. The 21mm socket works on Paccar MX 11 and MX 13 engines. Use with a 3/8” square drive.