If you notice play in the headset of D50/ST50, follow the instructions below.
Solution 1: Loosen the stem bolts slightly, then tighten the top cap bolt until there is no play, but ensure that the handlebars can still turn smoothly without binding.
If this doesn't solve the issue, head on to Solution 2:
Solution 2: Remove the headset cap, if you notice less than 3mm distance between stem and fork steering tube, add a 2.5mm or 3mm spacer (dia: 1-1/8" or 28.8mm). Tighten the cap first and then the stem bolts.