This is the WHS-300 Gauge with the alignment bar. The main plate is precision machined from a single block of aluminum and the surface is hard anodized to prevent damage from use. The alignment bar is made of precision machined steel.
When the bar is placed against the head, the white line indicates correct stroke. The width of the line indicates minimum to maximum stroke. The head should be exactly parallel with the rectangular end of the bar to align head zenith (tilt).