To get maximum legal performance in Briggs LO206 classes, you need to make sure the slide opens to the maximum.
These go no go gauges are .005" smaller than the maximum on one end and .001' under the maximum limit on the other end.
They are made that way ON PURPOSE so you can set the slide to to just under the maximum legal opening.
I suggest setting the slide using the .005" undersize and then check that the other (larger) end doesn't go.
This is a NEW version of the slide gauge. They are made this way so the main air bleed (that little brass tube) doesn't interfere with holding the gauge straight.
(SLIDE GAUGES ARE NOT USED ON ADULT MOTORS)