Honda CRF250F Owner's Manual Installation And Operation page 193

4. Check the chain slider (2), chain guide
slider (3) and chain roller (4) for wear.
If the chain slider and lower slider are
worn to the bottom of the cutouts (5),
have your dealer replace the slider.
Replace the chain guide slider if the
chain is visible through the wear
inspection window (6).
Replace the chain roller if it is smaller
than:
18 mm (0.7 in)
68
(5)
(6)
(2) Chain slider
(3) Chain guide slider
(4) Chain roller
(4)
(2)
(3)
(5) Cutout
(6) Wear inspection
window