Handlebar shims have always been part of the Hubjub toolkit for assembling the bike from your collection of components.
These are for solving various problems including accommodating traditional bars in oversize clamps.

22.2 - 25.4mm: aluminium anodised silver (current stock differs to photo and is not ridged).

25.4 - 31.8mm: aluminium and anodised black or silver

26.0 - 31.8 mm aluminium and anodised black

26.0 - 31.8mm: aluminium and anodised silver (four piece)