5/16" or 8mm. The 8mm are about 0.002" bigger stem diameter. Pretty close to the Magnum head diameter, but I think 0.020" bigger diameter, unless you get the 2.0" intake valves. Cost is a big advantage. Compared to a 318 LA intake valve, the LS valves are about 25 to 30 gm lighter. Then you toss in the beehive retainers that also save weight. The beehive spring is also lighter on the top end that moves, and has excellent resistance to resonance issues. You can generally pick up 500 RPM before valve float.
