VW / Audi water cooled 1.8L & 2.0L ARP 104-6004 Connecting Rod Bolts. ARP High Performance Wave-Loc Connecting Rod Bolts, 8740 Chromemoly Steel, The same heat-treated 8740 chrome moly steel is used to make these rod bolts as ARP’s standard High Performance rod bolts.
The big difference is in the shank design, with ARP’s exclusive (and patented) Wave-Loc technology providing substantial benefits. Because there are fairly wide tolerances in factory bolt holes, the bolt must be able to fit snugly and a knurl is applied. Unfortunately, these knurls cut deep into the bolt material, leaving sharp edges and enormous “stress risers” that promote failure. That’s why ARP developed the ARP Wave-Loc design that features symmetrical waves and provides an effective interference fit without creating stress risers in the bolt or the rod.