Zinc Plated Exhaust Springs, 100MM, 10Pk, These High Quality, Zinc Plated, Tempered Spring-Wire Exhaust Springs Use Economical One Piece Dedsign. 11 Sizes To Fit Most Exhaust Systems, From 57MM To 100MM. For Proper Measurement And Fitment Follow These Helpful Hints: 1) Exhaust Springs Should Be Measured Off The Vehichle. Always Wear Eye Protection When Removing And Insatalling Springs. 2) The Length Measurement Should Be Made From Inside Hook To Inside Hook. 3) For Correct Fit, Exhaust Springs Should Not Be Extended More Than 20% Of Free Length.