CR036 - 1/8" magnesium ultra-lite, axle collars.
For 1/8" axle / Hardbody racers, who like to keep their inline gear mesh, while testing different rear tires.
Not to be confused with heavier 4-40 screw, aluminum, or way heavier, 4-40 screw, plated brass ones.
Approximately .195" wide x .295" diameter.
Uses standard gear wrench, with your own favorite, 4-40 set screws.