Metric v Imperial conversions are not very good starting point. A lot of the bead manufacturers make both metric (in 0.5mm increments) and imperial (in X/8 or 16 or 32 or 64) - some mix and match similar sizes.
I personally prefer the 0.5mm metric increments for my beads.
5/64" = 2.0mm (close enough)
3/32" = actually 2.4mm
7/64" = actually 2.8mm
Since volume of a sphere is 4/3*Pi*r^3:
A true 2.5mm has 13% more volume than a 2.4mm
A true 3.0mm has 22% more volume than a 2.8mm
Here are some figures (These I weighed myself):
Type |
Size |
Mass (g) |
Tungsten-Slotted |
4.0 |
0.432 |
Tungsten-Slotted |
3.5 |
0.287 |
Tungsten-Slotted |
3.0 |
0.190 |
Tungsten-Slotted |
2.5 |
0.124 |
Tungsten-Slotted |
2.0 |
0.053 |
Tungsten-C/Sunk |
3.8 |
0.421 |
Tungsten-C/Sunk |
3.3 |
0.281 |
Tungsten-C/Sunk |
3.0 |
0.195 |
Tungsten-C/Sunk |
2.5 |
0.116 |
Tungsten-C/Sunk |
2.0 |
0.065 |
And material, as well as actual dia, hole/slot dia, countersunk cutout also make a big difference in overall mass.
In the above, the 2.0mm slotted actually has less mass than the 2.0mm countersunk - this I think is due to central hole size.
Weigh 10 beads to reduce error.
If you are going to compare using a powder scale - 1 grain = 0.065grams & most measure to 1/10 of a grain = 0.0065grams
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