Traditional unit in metric crafts is cm and the smallest traditional distance is 0.5 cm (pronounced "half" not "O point 5"). Notebook grid is 0.5 cm for example and you write and draw everything at shool on that grid so you get used to it (and get intuitive feel for how long a cm (2 grids) is in the process).
The dimensions you're mostly using are 0.5 cm, 1 cm, 1.5 cm, 2 cm, 2.5 cm, 5 cm, 10 cm.
> A quarter inch generally seems right for a small spacing.
A quarter inch is 6.35 mm compared to 5 mm (0.5 cm) which is basically the same for estetic purposes, any preference will be caused by familiarity more than any objective criteria.
> 1 inch and 1 half inch feels easier to keep in mind than 1 centimeter and 5 millimeters
Nobody says or thinks "1 centimeter and 5 millimeters" just like nobody says "I'm 1 meter and 80 centimeters tall". You're "180 centimeters tall" or (less often) "1.8 m tall".
There's even a word in my language "półtora" which means "one and a half", so 1.5 cm is just "półtora centymetra". But even with languages without this word people think "one and a half cm" not "one cm and five mm". You almost never mix units in metric in the same expression, it just makes everything difficult for no reason.
I think Americans don't understand that decimals are second nature to people using metric. When you write 1/2 we write 0.5 but we think the same - "half".
The dimensions you're mostly using are 0.5 cm, 1 cm, 1.5 cm, 2 cm, 2.5 cm, 5 cm, 10 cm.
> A quarter inch generally seems right for a small spacing.
A quarter inch is 6.35 mm compared to 5 mm (0.5 cm) which is basically the same for estetic purposes, any preference will be caused by familiarity more than any objective criteria.
> 1 inch and 1 half inch feels easier to keep in mind than 1 centimeter and 5 millimeters
Nobody says or thinks "1 centimeter and 5 millimeters" just like nobody says "I'm 1 meter and 80 centimeters tall". You're "180 centimeters tall" or (less often) "1.8 m tall".
There's even a word in my language "półtora" which means "one and a half", so 1.5 cm is just "półtora centymetra". But even with languages without this word people think "one and a half cm" not "one cm and five mm". You almost never mix units in metric in the same expression, it just makes everything difficult for no reason.
I think Americans don't understand that decimals are second nature to people using metric. When you write 1/2 we write 0.5 but we think the same - "half".