Designed with inbuilt spring lever to apply a gentle holding pressure on the line to prevent them sliding around.
8mm versions have a groove in the top surface to aid in identification as they are the same size externally.
6's and 9's can distinguished by the design where the numeral is aligned to the bottom of the part resulting in a slight flattening of the bottom of the 6 that is not present at the top of the 9. Its a slight difference but sufficient to tell them apart, if not enough they can always be printed in different colours.
I printed in black PETG, 0.20 layer height, 0.40 nozzle, then used a paint pen to highlight the numbers.
The author marked this model as their own original creation.