The last letter of the part number indicates the clearance of the ACL Race series engine bearings:
H = 0.0125mm (.0005”)
HX = 0.025mm (0.001”) - With extra clearance
HD = 0.0125mm (.0005”) -With location dowel holes
HXD = 0.025mm (0.001”) - With extra clearance and location dowel holes
ACL Engine bearings
ACL is the brand directly associated with high performance engine bearings. If you use "ACL bearings" -Then everyone know it is built with quality.