Clevite H-Series main bearings were developed primarily for NASCAR racing, but are well suited to other types of competition engines as well. They're especially good for engines that run at medium-to-high revs. They have steel backings with carefully selected overlays and a high crush factor, plus a medium level of eccentricity. H-Series bearings have enlarged chamfers at the sides for greater crank-fillet clearance and are made without flash plating for better seating. They are also available with either 180 degree or 360 degree oil grooves, as well as an extra 0.001 in. of clearance.