Solution might be to tape around the part of the bars where the stem sits (the white part on 3T bars), clear coat it and, while wet, sprinkle it with glitter or sand or whatever to make a non slip surface.
Or just use some gritty, grippy assembly paste?
Yes, that might be enough. And I already have that.
@Hulsroy started
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Or just use some gritty, grippy assembly paste?