This Wolff Light-Duty Coil Spring BlitzPack consists of 20 general purpose light-duty coil springs manufactured to metric standards. There are 10 different designs with 2 springs of each supplied. Springs are designed to function in 2.5mm to 7mm inside diameter openings and vary from 50mm to 100mm in overall length. This is a highly desirable assortment of springs, especially for repairs in foreign manufactured arms. Factory replacement parts are manufactured to the exact same specifications and tolerances and use the same manufacturing materials as the original parts. Some parts may require installation by a qualified gunsmith.