Requires Tim's lockring, spring and assembly tool (included slightly scaled versions that worked better for me, using PETG)
And 2 M3 bolts for a complete assembly.
UPDATE:
Added version 2 with more left offset, so the unit will be in the center of the handlebar.
And a version compatible with the Wahoo Bolt (tested with the Bolt V1).
Added modified springs which worked better for me (using PETG).
Also added an adapter for a 25.4mm handlebar (you need to print 2 pieces).
UPDATE (8 AUG 24):
Added version 3 with thicker handlebar grip.
UPDATE (19 DEC 24):
Larger bolt holes.
Added scaled version of lockring and assembly tool.
Removed older versions.
The author remixed this model.
Upfront handlebar mount.