Bolt Extractors 17 piece set includes sizes 4.00mm-8.00mm in 0.25mm increments. 16 piece set includes sizes 8.25mm-12.00mm in 0.25mm increments Removes rounded or damaged fasteners with any head configuration (hex, round, square) One-quarter millimeter increments between sizes ensures coverage, regardless of fastener head condition or manufacturer’s tolerance Manufactured from heat-treated alloy steel No hammering required to install socket over fastener; twist socket tightens as more torque is applied Additional applications include exhaust manifold nuts, studs, pipe nipples and corroded marine fasteners. Each set comes packaged on sturdy, professional-grade locking socket rail All product, including socket rails, made in USA