This is a five-sided die, with the special feature of clearly showing the value on a flat surface, face-up.
The roller is based on a Reuleaux pentagon, which has very good rolling characteristics.
The numbers are sized such that the same amount of material is present in each face.
About this set
This metal form is a 1mm stainless steel shell with a hollow interior. Together with the rounded shape, this gives the dice a very pleasant feel and weight for rolling. They roll extremely well, and stop well centred on the faces. The ends have the round holes which gave this set of dice their name.
The digits are quite clear enough to view at a glance in plain stainless steel. Polished bronze steel is perhaps slightly less visible. If the numbers are not clear enough for you it is straightforward to enhance them by adding a small amount of a contrasting paint, then wiping off the excess.
I thought long and hard about the order of the sides for this die. While standard dice have opposing sides summing to a constant, that is impossible here - because there is no facing side.
I elected to minimise the variation of 'sum of adjacent face pairs', using the order : 1 4 3 2 5. This order has the property of odd positions increasing and even positions decreasing from left-to-right, which is also the case in my seven-sided die.